As of July 10, 2020

American Conference on Neutron Scattering

Hard Condensed Matter

* Invited Paper

SESSION B02.01: Magnetic symmetries are tuned.

Interaction in Rare Earth Magnets [1] Paddison, Joseph AM, Marcus Daum, Zhiling Dun, Georg Ehlers, Yaohua Liu, Matthew B. Stone, Haidong Zhou, and Martin Mourigal. "Continuous excitations of the triangular-lattice quantum spin B02.01.01* liquid YbMgGaO 4." Nature Physics 13, no. 2 Quantum Disorder and Unconventional (2017): 117-122. Magnetism in ARO2 (A=Alkali Metal, R=Rare [2] Bordelon, Mitchell M., Eric Kenney, Chunxiao Earth Metal) Liu, Tom Hogan, Lorenzo Posthuma, Marzieh Stephen D. Wilson; University of California, Santa Kavand, Yuanqi Lyu et al. "Field-tunable quantum Barbara, United States disordered ground state in the triangular-lattice antiferromagnet NaYbO 2." Nature Physics 15, no. Triangular lattice compounds decorated with 10 (2019): 1058-1064. anisotropic Jeff=1/2 moments have received [3] Rawl, R., L. Ge, H. Agrawal, Y. Kamiya, CR revitalized interest due to experimental reports of Dela Cruz, Nicholas P. Butch, X. F. Sun et al. "Ba 8 quantum disordered ground states in classes of CoNb 6 O 24: A spin-1/2 triangular-lattice layered materials such as YbMgGaO4 [1], Heisenberg antiferromagnet in the two-dimensional NaYbO2 [2], Ba8CoNb6O24 [3] and other related limit." Physical Review B 95, no. 6 (2017): 060412. compounds. Among these, a series of Yb-based compounds of the form NaYbX2 (X=O, S, Se) have B02.01.02 emerged as structurally ideal platforms A Novel Strongly Spin-Orbit Coupled Quantum featuring Jeff=1/2 Yb moments that derive from well- Dimer Magnet—Yb2Si2O7 1 1 isolated Kramers crystal-field doublets. A broad Gavin L. Hester , Harikrishnan S. Nair , Timothy R. 1 1 1 spectrum of these systems fail to establish static Reeder , Danielle Yahne , Tim DeLazzer , Leo 2 2 1 magnetic order, despite an enhanced exchange field Berges , Djamel Ziat , James R. Neilson , Adam 3 3 2 due to relatively close Yb-Yb distances. Uniquely, Aczel , Gabriele Sala , Jeff Quilliam and Kate 1,4 1 these materials can also be driven into an Ross ; Colorado State University, United 2 3 intermediate, fluctuation-driven antiferromagnetic States; Université de Sherbrooke, Canada; Oak state under modest, accessible magnetic fields. This Ridge National Laboratory, United States; 4 opens the phase boundary between native quantum CIFAR, Canada disorder and fluctuation-driven order to experimental exploration with neutron scattering and other The quantum dimer magnet (QDM) is the canonical techniques. In this talk, I will present our work in example of quantum magnetism. The QDM state NaYbO2 exploring the magnetic ground state as well consists of entangled nearest-neighbor spin dimers as its evolution into a collinear up-up-down state and often exhibits a field-induced triplon Bose- under applied magnetic field. I will also discuss some Einstein condensate (BEC) phase. Many compounds 2+ 2+ our recent work studying related ARO2 compounds based on 3d magnetic cations (Cu , Ni ) have been with alternative R-site species and structure-types. found that exhibit a quantum dimer state with a BEC The goal will be to illustrate the spectrum of phase. Due to the energy scales of 3d magnetism, the unconventional magnetic states realized across this critical fields of previous QDM systems with a BEC class of materials as the R-site cation and lattice phase are often above the common field capabilities at neutron sources ( 15 T). We have found a new CePd3 and which can be attributed to particle-hole QDM in the strongly spin-orbit coupled, distorted excitations in a coherent itinerant 4f correlated honeycomb lattice material∼ Yb2Si2O7 which exhibits ground state. The Q-dependence disappears as the a “dome” of field-induced magnetic ordering in the temperature is raised and the 4f electron bandstates field vs. temperature phase diagram, reminiscent of a become increasingly incoherent. The measured BEC phase, with exceptionally low critical fields of phonons can be described adequately by a calculation Hc1 0.4 and Hc2 1.4 T. Our single crystal neutron based on standard band theory, without recourse to scattering, specific heat, and ultrasound velocity 4f correlations. A low temperature magnetic peak at ~ measurements∼ reveal∼ a gapped singlet ground state at 30meV shows dispersion identical to an optic phonon zero field with sharp, dispersive excitations and an branch. This 4f/phonon resonance disappears as the absence of magnetic ordering. Using inelastic neutron temperature is raised. The phonons appear to remain scattering in an applied magnetic field we observe a unaffected by the resonance. We speculate that this Goldstone mode (gapless to within 0.037 meV) that unusual excitation arises from the large amplitude persists throughout the entire field induced beating of the light Al atoms against the heavy Yb magnetically ordered phase, suggestive of the atoms, resulting in an oscillation of the spontaneous breaking of U(1) symmetry expected for 4f/3p hybridization that underlies the heavy fermion a triplon BEC. However, in contrast to other well- physics. known cases of this phase, the high-field (μ0H ≥ 1.2 T) part of the phase diagram in Yb2Si2O7 is B02.01.04 interrupted by an unusual regime signaled by a Crystal Field Splitting and Spin Hamiltonian of change in the field dependence of the ultrasound the Quantum Magnet YbCl3 velocity and magnetization, as well as the Gabriele Sala1, Matthew Stone1, Binod Rai1, Andrew disappearance of a sharp anomaly in the specific heat. May1, David Parker1, Gabor Halasz1, Pontus Laurell1, Inelastic neutron scattering data obtained in the high- Nicholas Butch2, Yongqiang Cheng1, Georg Ehlers1, 1 1 3 field regime (μ0H = 3 T) was fit using linear spin Ovidiu Garlea , Qiang Zhang , Ganesh Pokharel , wave theory as implemented by the Matlab package, Hasitha Suria Arachchige3, David Mandrus3, Mark L. SpinW. Contrary to the expectations for a highly Lumsden1 and Andrew D. Christianson1; 1Oak Ridge spin-orbit coupled compound, the fit indicates that National Laboratory, United States; 2National Yb2Si2O7 exhibits predominantly isotropic Institute of Standards and Technology, United 3 (Heisenberg) exchange. This adds Yb2Si2O7 to the States; The University of Tennessee, Knoxville, growing roster of Yb-based compounds that exhibit United States dominant Heisenberg exchange. Our measurements provide the opportunity to further study how YbCl3 is a nearly ideal honeycomb lattice quantum predominantly isotropic exchange develops in a magnet. We have studied YbCl3 with a combination strongly spin-orbit coupled system and to bring the of neutron scattering, magnetic susceptibility, and full power of neutron scattering to bear on the entire heat capacity measurements. We determine the phase diagram of a BEC compound. crystal field Hamiltonian through simultaneous refinements of the inelastic neutron scattering and B02.01.03 magnetization data. The ground state doublet of the Q-Dependent Kondo Spin Fluctuations and a crystal field Hamiltonian is well isolated and results 4f/Phonon Resonance in the Intermediate Valent in an effective spin-1/2 system with local easy plane Compound YbAl3 anisotropy at low temperature. The low energy Jon Lawrence1,2, Andrew D. Christianson3, Victor excitation spectrum reflecting the collective 3 3 4 1 Fanelli , Lucas Lindsay and Sai Mu ; University of properties of YbCl3 shows strong quantum effects California, Irvine, United States; 2Los Alamos which can be explained by a spin wave theory on an National Laboratory, United States; 3Oak Ridge ideal honeycomb lattice. In particular, we are able to National Laboratory, United States; 4University of identify and explain a novel sharp multimagnon California, Santa Barbara, United States feature occurring atop the multimagnon continuum.

The intermediate valence (IV) compound B02.01.05 14- YbAl3 exhibits nonintegral valence (Yb 4f Magnetic Short-Range Correlations and n z f(5d6s) where z = 2+nf = 2.75) in a moderately Continuous Transitions in TmMgGaO4 1 1 2 heavy (m* ~ 20-30me) ground state with a large Zhiling Dun , Marcus Daum , Huibo Cao , Henry 3 2 4 Kondo temperature (TK ~ 600K). We have measured Fischer , Yaohua Liu , Haidong Zhou , Benjamin a single crystal of this material on the ARCS Frandsen5 and Martin Mourigal1; 1Georgia Institute spectrometer at the Spallation Neutron Source. We of Technology, Georgia; 2Oak Ridge National find that at low temperature, the Kondo-scale spin Laboratory, United States; fluctuations have a momentum (Q) dependence 3Institut Laue-Langevin, France; 4The University of similar to that seen recently in the IV compound Tennessee, Knoxville, United States; 5Brigham Young University, United States the paramagnetic phase. I proceed by simulating diffraction data for a range of bond-dependent The rare-earth triangular antiferromagnet models (test cases) on triangular and honeycomb RMgGaO4 is an exciting platform for quantum lattices [8]. I show that simulated paramagnetic magnet studies. For R = Yb, experiments have neutron-diffraction data contain distinctive signatures evidenced a spin-liquid-like behavior at low of the signs of bond-dependent interactions, which temperature whose origin is still under debate. For can therefore be “read” directly from the data. I R=Tm, the system is a promising candidate to realize further demonstrate that, in every test case, values of transverse Ising model based on non-Kramers the bond-dependent interactions can be accurately Tm3+ ion and an effective transverse field originating determined via unconstrained fits, and that this from crystal electric field. Recent theoretical work approach is robust to the level of statistical noise has predicted two continuous Kosterlitz-Thouless typical of real measurements. Perhaps most (KT) transitions at 4 K and 1 K, respectively. Using surprisingly, powder averaging does not entirely AC susceptibility, neutron diffraction, and magnetic remove this sensitivity to bond-dependent pair-distribution function measurements, we unveil interactions; consequently, powder-diffraction data the two broad transitions in TmMgGaO4 from can constrain such interactions when single-crystal analysis of scattering results in momentum- and real- samples are unavailable. I conclude by discussing the space, respectively. We found that short-range three- advantages, limitations, and possible applications of sublattice magnetic correlations develop over a broad this approach, and discuss my results in the context temperature range while cooling and eventually of developments in reverse Monte Carlo refinement concentrate into quasi-long-range magnetic Bragg [9], pair distribution function analysis [10], and peaks at the K-point of the triangular Brillion zone. machine learning [11]. Furthermore, our data suggests that the local structural disorder that is inescapable in the [1] Kitaev, Ann. Phys. 303, 2 (2003); [2] Zhu et RMgGaO4 structure, plays a minimal role in the zero- al., Phys. Rev. Lett. 120, 207203 (2018); [3] field limit, but strongly affect the collective Takagi et al., Nat. Rev. Phys. 1, 264 (2019); [4] magnetism under external magnetic fields. Broholm et al., Science 367, eaay0668 (2020); [5] *The work at Georgia Tech was sponsored by the Laurell and Okamoto, npj Quantum Mater. 5, 2 National Science Foundation under NSF-DMR- (2020); [6] Banerjee et al., Nat. Mater. 15, 733 1750186 (2016); [7] Ran et al., Phys. Rev. Lett. 118, 107203 (2017); [8] Chaloupka and Khaliullin, Phys. Rev. B 92, 024413 (2015); [9] Paddison and B02.01.07 Goodwin, Phys. Rev. Lett. 108, 017204 (2012); [10] Scattering Signatures of Bond-Dependent Frandsen, Yang, and Billinge, Acta Crystallogr. A 70, Magnetic Interactions 3 (2014); [11] Samarakoon et al., Nat. Commun. 11, Joe Paddison; Oak Ridge National Laboratory, 892 (2020). United States This work was supported by Oak Ridge National Bond-dependent interactions can generate exotic Laboratory's LDRD program (#10004); the U.S. topological states such as Kitaev and frustrated spin Department of Energy, Office of Science, Basic liquids [1,2]. Materials that realize such states have Energy Sciences, Materials Sciences and Engineering potential applications for topological quantum Division; and Churchill College, University of computation, and are of fundamental interest because Cambridge. they can show entangled ground states whose excitations have fractional quantum numbers [3,4]. Experimentally determining the values of bond- dependent interactions is key to identifying the most SESSION B02.02: Perovskites and promising topological materials. However, such interactions are challenging to measure, for two main Related Materials reasons [5]. First, most experiments are sensitive only to a subset of the key interactions. Second, current data-analysis approaches typically assume a state B02.02.01* with conventional long-range magnetic order — e.g., Electrolyte-Gate-Controlled Magnetism in to model magnon spectra [6,7] — but this Perovskite Oxides Probed by Operando Polarized requirement is problematic because conventional Neutron Reflectometry magnetic ordering is not expected in topological Jeffery Walter1,2, Vipul Chaturvedi1, Helin Wang1, states [4]. In this talk, I explore the extent to which Joey Gotchnik1, Alexander J. Grutter3, Brian J. bond-dependent interactions can be extracted from Kirby3, Julie A. Borchers3, Timothy R. Charlton4, magnetic neutron-diffraction patterns measured in Haile Ambaye4, Michael Fitzsimmons4,5, Biqiong Yu1, Guichuan Yu1, Martin Greven1, Peter Orth6, and C. Leighton, Phys. Rev. Materials 1, 071403(R) Rafael Fernandes1, Boris Shklovskii1, Turan Birol1, (2017). Zhan Zhang7, Hua Zhou7, John W. [4] B. Yu, G. Yu, J. Walter, V. Chaturvedi, J. Freeland7 and Chris Leighton1; 1University of Gotchnik, J.W. Freeland, C. Leighton and M. Minnesota, United States; 2Augsburg University, Greven, submitted, Appl. Phys. Lett (2019) United States; (arXiv:1911.07139) 3National Institute of Standards and Technology, [5] P.P. Orth, R.M. Fernandes, J. Walter, C. Leighton United States; 4Oak Ridge National Laboratory, and B.I. Shklovskii, Phys. Rev. Lett. 118, 106801 United States; (2017). 5The University of Tennessee, Knoxville, United [6] J. Walter, T. Charlton, H. Ambaye, M. States; 6Iowa State University, United Fitzsimmons, P.Orth, R. Fernandes, and C. States; 7Argonne National Laboratory, United States Leighton, Phys. Rev. Materials 2, 111406(R) (2018).

Recently, incorporation of electrolytes such as ionic B02.02.02* liquids into field-effect transistors has enabled Tuning Chemical Short Range Order in the Solid electric double layer transistors (EDLTs) capable of State inducing very large (up to 1015 cm-2) charge carrier Katharine Page1,2; 1Oak Ridge National Laboratory, densities at surfaces. This correspond to significant United States; 2The University of Tennessee, fractions of an electron or hole per unit cell in most Knoxville, United States materials, sufficient to electrically control electronic/magnetic phase transitions. While It is widely recognized in catalysis, energy storage this has stimulated great interest, many challenges and conversion, and a wide array of other functional remain, including understanding the true mechanisms materials areas that unique properties and (i.e., electrostatic vs. electrochemical [1]), characteristics are governed by intricate structural- developing operando characterization methods, and chemical relationships. Locally ordered cation and assessing the full power and universality of the anion motifs offer a gamut of possibilities but remain approach. Here, I will present our recent work a challenge because experimental tools to observe applying electrolyte gating using solid ion gels [1-6] them are limited. We present recent efforts to apply to magnetic complex oxides (e.g., La1-xSrxCoO3-δ), and extend neutron and X-ray total scattering and focused on electrical control of magnetism, related probes to explore chemical short range probed via operando polarized neutron reflectometry order and associated structure-property responses in (PNR). Our findings greatly clarify the issue of solid state materials. First, we will present our work electrostatic vs. electrochemical response, uncovering universal B-site cation ordering in mixed culminating in a picture where electrostatic gating vs. metal inverse spinel oxides, materials of interest as oxygen vacancy creation/annihilation can be high voltage cathodes in Li-ion batteries. It is found understood and predicted based on bias polarity, and that the degree and length-scale of cation order the enthalpy of formation and diffusivity of oxygen depend on the charge and ionic radii difference vacancies [1-6]. Critically, this was between constituents, unifying the view of many achieved via development of operando probes, observed physical properties in the structural particularly PNR [3,6], synchrotron X-ray diffraction archetype. Ongoing efforts to increase the [3], and X-ray absorption spectroscopy/magnetic reversibility of charge-discharge chemistries will be circular dichroism (XAS/XMCD) [4]. Most described. Second, we will present structure-property significantly, electrical control of the Curie characteristics of pyrochlore Ln2M2O7 materials, a temperature in La1-xSrxCoO3-δ has been demonstrated new family in the emerging class of high entropy over a ~200 K window by an electrochemical oxides (HEOs). HEOs exhibit a single-phase crystal mechanism [3] and over a record 160 K window by structure containing five or more different metal electrostatic gating [6]. In both cases PNR has been cations of the same amount on single crystallographic used as an operando probe of the electrically- lattice sites. The resulting configurational disorder controlled ferromagnetism, generating insight far promises unique property characteristics, such as beyond transport alone. increased structural stability (by impairing the Work supported by the US Department of Energy migration of defects) and multi-functional “cocktail” through the University of Minnesota Center for effects (through high numbers of possible element Quantum Materials. combinations and their interactions). We combine numerous local structure probes and a complex [1] C. Leighton, Nat. Mater. 18, 13 (2019). modeling framework to explore the characteristics [2] J. Walter, H. Wang, B. Luo and C. Leighton, ACS that specific participating cations and synthesis Nano 10, 7799 (2016). conditions impart to the family, demonstrating a rich [3] J. Walter, G. Yu, B. Yu, A. Grutter, B. Kirby, J. tunability of associated properties. These examples Borchers, Z. Zhang, H. Zhou, T. Birol, M. Greven highlight a broader theme of our research aimed at extracting crystal structure models from experimental the tetragonal material LiHoF4 and its disordered data with the detail needed to guide and validate solid variant LiHoxY1-xF4 [2]. The disordered TFIM state theories, and design new and improved provides a complex optimization problem, where the functional materials. Current challenges and future ground state of the system can be reached more opportunities in this arena will be discussed. efficiently by quantum fluctuations that induce tunneling under an applied transverse field. This has B02.02.03 already been observed, through ac magnetic Diffuse Neutron and X-Ray Scattering from susceptometry, in the magnetically diluted form Cesium Lead Bromide LiHoxY1-xF4 (x=0.44) [3], however, without Matthew J. Krogstad1, Alex Rettie2, Stephan gaining direct information on the microscopic spin Rosenkranz1, Duck Young Chung1, Mercouri correlations that are involved, i.e. the quantity that is Kanatzidis3, Feng Ye4, Xing He5, Olivier actually being optimized. We report on details of the Delaire5 and Raymond Osborn1; 1Argonne National microscopic spin correlations via a measurement of Laboratory, United States; 2University College elastic diffuse magnetic neutron scattering in three London, United Kingdom; 3Northwestern University, dimensions. United States; 4Oak Ridge National Laboratory, United States; 5Duke University, United States [1] A. Dutta, G. Aeppli, B.K. Chakrabarti, U. Divakaran, T.F. Rosenbaum, and D. Sen. Quantum Cesium lead bromide has attracted recent attention, Phase Transitions in Transverse Field Spin Models: along with other lead halide perovskites, due to its From Statistical Physics to Quantum Information. optoelectronic properties. It has been proposed that Cambridge Univ. Press (2015). the long carrier lifetime supporting these properties is [2] M.J.P. Gingras, P. Henelius, Collective due to local structural fluctuations. To investigate the Phenomena in the LiHoxY1-xF4 Quantum Ising short-range lattice distortions that such fluctuations Magnet: Recent Progress and Open Questions. J. would imply, diffuse neutron and x-ray scattering Phys.: Conf. Ser. 320 012001 (2011). experiments were performed on single crystals of [3] J. Brooke, D. Bitko, T.F. Rosenbaum, and G. CsPbBr3 across a range of temperatures spanning the Aeppli. Quantum Annealing of a Disordered Magnet. two structural phase transitions. Significant diffuse Science, 284(5415):779–781 (1999). scattering indicating two-dimensional deviations from the average crystals structure was observed in B02.02.05 both higher-temperature phases, indicating that local Realization of the Orbital-Selective Mott State at planar distortions remain present at these higher the Molecular Level in Ba3LaRu2O9 temperatures. Distinct elastic and inelastic features, Adam Aczel1,2, Qiang Chen2 and Haidong distinguishing between static and dynamic forms of Zhou2; 1Oak Ridge National Laboratory, United local displacement correlations, were found in the States; 2University of Tennessee, United States neutron scattering data collected at CORELLI, with the short-range planar distortions shown to be quasi- Molecular magnets based on heavy transition metals static in nature. Models of locally correlated atomic have recently attracted significant interest in the quest displacements are able reproduce the observed for novel magnetic properties. For systems with an diffuse scattering, emphasizing the importance of odd number of valence electrons per molecule, high local displacement in understanding the structure of or low molecular spin states are typically expected in this material. This work was supported by the US the double exchange or quasi-molecular orbital limits DOE, Office of Science, Basic Energy Science, respectively. In this talk, we use bulk Materials Sciences and Engineering Division. characterization, muon spin relaxation, neutron diffraction, and inelastic neutron scattering to identify B02.02.04 a rare intermediate spin-3/2 per dimer state that In Search of Microscopics of Quantum Annealing cannot be understood in a double exchange or quasi- Steffen Säubert1, Colin Sarkis1, Feng Ye2 and Kate molecular orbital picture and instead arises from Ross1,3; 1Colorado State University, United orbital-selective Mott insulating behavior at the States; 2Oak Ridge National Laboratory, United molecular level. Our measurements are also States; 3CIFAR, Canada indicative of stripe magnetic order below TN = 25 K for these molecular spin-3/2 degrees-of-freedom, Quantum annealing refers to a method for solving which is consistent with expectations for an ideal optimization problems through quantum fluctuations triangular lattice with significant next nearest rather than the more traditional thermal fluctuations neighbor in-plane exchange. Finally, we present and has been argued to produce a speed-up for some neutron diffraction and Raman spectroscopy data complex optimization problems [1]. A model system under applied pressure that reveal a coincident crystal to study quantum annealing is the transverse field symmetry lowering and spin state transition from S = Ising model (TFIM) that is experimentally realized in 3/2 to S = 1/2 at a modest pressure of ~ 1 GPa, which highlights the delicate balance between competing with single crystal neutron scattering. Recent energy scales in this system. inelastic and in-field elastic neutron scattering results will also be discussed. Sizable single crystals of QSL candidate Zn-substituted barlowite (Cu3.44Zn0.56(OH)6FBr) were grown for the first time SESSION B02.03: Frustrated and compared to Cu3.05Zn0.95(OH)6FBr and herbertsmithite. Significantly, no magnetic transition Magnets is observed down to T=0.1K, indicating a surprising robustness of the QSL against interlayer Cu2+ impurities. These samples span a spectrum of quantum spin liquidity, allowing this exotic ground B02.03.01* state to be probed systematically. Materializing Rival Ground States in the Barlowite Family of Kagome Magnets B02.03.02 1,2 1,2 1,2 Rebecca Smaha , Wei He , Jack M. Jiang , Jiajia Emergent Quasi-Spin Anisotropy in Highly 2 2 2 Wen , Yi-Fan Jiang , John P. Sheckelton , Charles J. Frustrated Pseudobrookite Fe2TiO5 1 3 3 Titus , Suyin G. Wang , Yu-Sheng Chen , Simon J. P. G. LaBarre1, Daniel Phelan2, Y. Xin3, Feng Ye4, 4 5,6 7,8 7 Teat , Adam Aczel , Yang Zhao , Guangyong Xu , Daniel M. Pajerowski4, T. Siegrist5,3, Stephan 7 2 Jeffrey W. Lynn , Hong-Chen Jiang and Young S. Rosenkranz2 and A. P. Ramirez1; 1University of 1,2 1 2 Lee ; Stanford University, United States; SLAC California, United States; 2Argonne National 3 National Accelerator Laboratory, United States; The Laboratory, United States; 3National High Magnetic 4 University of Chicago, United States; Lawrence Field Laboratory, United States; 4Oak Ridge National 5 Berkeley National Laboratory, United States; Oak Laboratory, United States; 5FAMU-FSU College of 6 Ridge National Laboratory, United States; The Engineering, United States University of Tennessee, Knoxville, United 7 States; National Institute of Standards and Magnetic anisotropy is essential for many 8 Technology, United States; University of Maryland, applications and has recently also been a focal point College Park, United States of fundamental importance as it can play a pivotal role in quantum spin liquids. Such anisotropy Quantum magnets display exotic phases that may be originates from the combined effects of orbital strongly influenced by small differences in structure occupation, spatial anisotropy, and spin-orbit and composition. The quantum spin liquid (QSL) is coupling. In spin glasses, anisotropy is usually an unusual magnetic ground state, characterized by considered single-ion-like, that is, it exists long-range quantum entanglement of the spins but a independent of spin-spin interactions and anisotropy lack of long-range magnetic order down to T=0K. exists above the freezing temperature. An s-state ion This is believed to be possible in highly frustrated of a half-filled shell, such as Fe3+, on the other hand spin-1/2 systems, so materials with a kagome is completely isotropic since it’s wave function has 2+ arrangement of Cu ions are prime candidates. We no orbital character, though second order effects due find that when the bonds of the kagome lattice are to virtual interactions with non-half-filled ions exist. modulated with a periodic pattern, new quantum Since for such systems there is expected to be very ground states emerge. Newly synthesized crystalline small, if any, anisotropy, it is surprising that barlowite (Cu4(OH)6FBr) and Zn-substituted Fe2TiO5 exhibits highly anisotropic responses both barlowite demonstrate the delicate interplay between below and above the spin glass freezing temperature singlet states and spin order on the spin-1/2 kagome Tf ~ 55K. This compound crystallizes in the lattice. Comprehensive structural and magnetic orthorhombic pseudobrookite structure with close to measurements (including single crystal and powder completely random mixing among Fe3+ and Ti4+ ions. X-ray diffraction, powder neutron diffraction, and While attempts to explain the observed Ising-like single crystal neutron scattering) were performed to anisotropy in the susceptibility above Tf and the address open questions about their crystal and absence of any freezing anomaly in the plane magnetic structures. We reveal a clear structure- perpendicular to the Ising axis at Tf were based on the properties relationship between two variants of phenomenological introduction of anisotropy, its barlowite with distinct low-temperature structures. origin remained unexplained. In order to obtain a Our novel single crystalline barlowite has a subtle detailed understanding of these puzzling symmetry lowering, and its kagome lattice contains a observations, we utilized single crystal diffuse and motif of distorted and undistorted triangles, for which inelastic neutron scattering to investigate in detail the numerical simulations predict a pinwheel valence spin correlations. Upon cooling towards the freezing bond crystal state instead of a QSL state. The temperature, we observe the growth of streaks of presence of interlayer spins eventually leads to novel highly anisotropic diffuse magnetic scattering, which pinwheel q=0 magnetic order, which we elucidate evidence the growth of surfboard-shaped regions of correlated spins: while spins are strongly correlated B02.03.04 along an axis perpendicular to the Ising-axis with a The Structure Factor Studies of the Ising Shastry correlation length extending over ten unit cells in the Sutherland Model Revealed Using Quantum spin glass state, along the Ising axis the correlation Annealing length is about four times smaller and along the Arnab Banerjee1, Paul Kairys2, Travis Humble3, Jack remaining axis, spins are only correlated over one or Raymond4 and Andrew King4; 1Purdue University, two nearest neighbors. The comparison of energy- United States; 2The University of Tennessee, integrated to elastic only scattering shows that Knoxville, United States; 3Oak Ridge National substantial fluctuations remain present at the lowest Laboratory, United States; 4D-Wave Systems, temperature measured, and inelastic measurements Canada indeed reveal spin excitations extending to at least 10meV. We will discuss that these surfboards form The macroscopic properties of a material depend on nanoscale antiferromagnets that mimic the behavior the strengths and symmetries of the microscopic of an XY spin system, and that the transverse Hamiltonian which can be tuned both by an external fluctuations of these XY quasi-spins are the “quasi- stimulus, such as a magnetic field or due to intrinsic spin” degrees of freedom that freeze. We therefore disorder. Understanding and tuning the phases of suggest that the Ising anisotropy observed in matter and their transitions is in the heart of modern Fe2TiO5 is an emergent property, driven by material science. In this theoretical work, we interactions among atomic spins. This work was establish a quantum hardware route to understanding supported by the US DOE, Office of Science, Basic phases of materials by successfully computing of the Energy Science, Materials Sciences and Engineering phases of a 468-spin Shastry-Sutherland Hamiltonian Division. on a 2000 qubit D-Wave Quantum Annealer. We formulate a new approach that rely on iterative quantum annealing of a model Hamiltonian to B02.03.03 improve computational convergence. We introduce a SU(3) Magnetic Excitations of the Frustrated novel use of mean-field boundary conditions to tune Ising Magnet FeI2 the effects of disorder within the chip to mimic Martin Mourigal; Georgia Institute of Technology, physical disorder in real materials and to mitigate the United States errors from finite system size. We not only recover four distinct phases predicted by Monte Carlo, We present a detailed investigation of the spin including the well-known transition to a fractional dynamics in single-crystals of the layered spin-one magnetization plateau, within a very small number of triangular-lattice compound FeI2. Previous thermo- iterations but also identify the critical behavior at magnetic measurements revealed a strong Ising their transitions as well as the effects from disorder. single-ion anisotropy for the Fe2+ ions in FeI2 and a Our results establish quantum annealing to provide a magnetically long-range ordered state below 9.3K, viable and accurate description of the ground state of which can be understood from the competition magnetic Hamiltonians, providing an exciting between nearest neighbor ferromagnetic interactions pathway to understanding data obtained from neutron and a complex set of further-neighbor interactions. scattering experiments on real spintronic materials. Early neutron scattering, far-infrared and ESR measurements, revealed the emergence of a two- B02.03.05 magnon bound state (TMBS) as the lowest energy Electric Current Control of the Spin-Orbit mode from this ordered state. The TMBS carries an Coupled 4d Ruthenate Ca2Ru0.97Mn0.03O4 apparent g-factor that is doubled compared to that of Feng Ye1, Christina Hoffmann1, Hengdi Zhao2 and single magnon excitations, which can be explained Gang Cao2; 1Oak Ridge National Laboratory, United by a change of 2 units in spin angular momentum, at States; 2University of Colorado Boulder, United odds with the dipole selection rule. We revisit the States spin excitations of FeI2 using modern neutron- scattering instrumentation and map out the magnetic The unique interplay between spin-orbit interaction structure, diffuse scattering and low-energy magnetic (SOI) and Coulomb correlation (U) in 4d/5d oxides excitation spectrum. We extract a model Hamiltonian drives unusual physical behavior. Novel for FeI2 and elucidate a novel hybridization nonequilibrium phenomena can be further induced by mechanism that quantitatively explains current and external stimuli including synchrotron x-ray, previous spectroscopic experiments on this enigmatic magnetic field, and electric current [1–3]. In this talk, compound. The work at Georgia Tech was sponsored I will present neutron diffraction study of the quasi- by the Department of Energy under DE-SC-0018660. two-dimensional Mott Ca2Ru0.97Mn0.03O4, which shows dramatic reduction of the electric resistivity, suppression of the antiferromagnetic transition, and induction of new orbital order above critical current density. Our in-situ structural characterization crystals of Yb2Ge2O7 grown by a hydrothermal implies that the in-plane orthorhombicity diminishes method. Comparison of field-polarized INS data with with increasing current density, accompanied by the linear Spin-wave calculations allowed the straightened of the Ru-O-Ru bonding angles. The determination of the four symmetry allowed temperature-current phase diagram establishes an exchange parameters for Yb2Ge2O7. The g-tensor was intimate correlation between the lattice and electronic independently determined from electron structure in this nonequilibrium, steady state driven paramagnetic resonance on a by current [4]. Our results shed light to the nature of Lu1.98Yb0.02Ge2O7 sample in order to enable an the Mott-Insulator transition and provide key unambiguous determination of these parameters. Our information for the emerging phenomena near the analysis and theoretical modeling place Yb2Ge2O7 in transition. extreme proximity to the classical phase boundary [1] C. Sow, S. Yonezawa, S. Kitamura, et al., between the AFM and FM phase, lending strong Science 358, 1084 (2017). support to the notion of phase competition as playing [2] J. Bertinshaw, N. Gurung, P. Jorba, et al., Phys. a key role in the Yb pyrochlore family. DOE:DE- Rev. Lett. 123, 137204 (2019). SC0020071 [3] C. Sow, R. Numasaki, G. Mattoni, et al., Phys. Rev. Lett. 122, 196602 (2019). B03.01.02 [4] H. Zhao, B. Hu, F. Ye, et al., Phys. Rev. B 100, Pseudo-Spin Versus Magnetic Dipole Moment 241104 (2019). Ordering in the Isosceles Triangular Lattice Material K3Er(VO4)2 Danielle Yahne1, Liurukara Sanjeewa2, Athena Sefat2, Bradley S. Stadelman3, Joseph Kolis3, Stuart SESSION B03.01: Student Research Calder2 and Kate Ross1,4; 1Colorado State University, United States; 2Oak Ridge National Laboratory, Spotlight United States; 3Clemson University, United States; 4CIFAR, Canada

B03.01.01* Spin-½ antiferromagnetic triangular lattice models Unravelling Competing Microscopic Interactions are the quintessential example of geometric at a Phase Boundary—A Single Crystal Study of frustration, with the nature of anisotropies in the the Metastable Antiferromagnetic Pyrochlore model revealing a variety of different ground states Yb2Ge2O7 and quantum effects. Strong spin-orbit coupling and Colin Sarkis1, Jeff Rau2,3, Duminda Sanjeewa4, crystal field effects can cause the rare-earth ions to Matthew Powell4, Joseph Kolis4, Jonathon Marbey5, form pseudo-spin-½ magnetic moments with Stephen Hill5, Jose A. Rodriguez-Rivera6, anisotropic single-ion and exchange properties. Thus, Harikrishnan S. Nair1, Michel Gingras7 and Kate rare-earth based triangular lattices are an interesting Ross1; 1Colorado State University, United playground to explore the interplay between States; 2University of Windsor, Canada; 3Max Planck frustration and anisotropy. Here we study one such Institute, Germany; 4Clemson University, United case, the rare-earth double vanadate glaserite material States; 5Florida State University, United K3Er(VO4)2, which is a quasi-2D isosceles triangular States; 6National Institute of Standards and antiferromagnet. Our specific heat and neutron Technology, United States; 7University of Waterloo, powder diffraction data from K3Er(VO4)2 reveal a Canada transition to long-range magnetic order at TN = 155 ± 5 mK, recovering all Rln(2) entropy. A Warren-like Rare earth pyrochlore oxides have been found to be Bragg peak profile in addition to 3D ordered Bragg hosts for a wide breadth of exotic phenomena based peaks indicates a coexistence of 2D and 3D magnetic on strong frustration. Studies on single crystals of correlations below TN. Our magnetic susceptibility 3+ Yb2Ti2O7 have established that it forms a data reveals that Er takes on a strong XY single-ion ferromagnetic (FM) ground state, but lies near a anisotropy in K3Er(VO4)2, and therefore should classical phase boundary between FM and contain the majority of the moment within the ab- antiferromagnetic (AFM) states. Meanwhile, powder plane. Considering this, in conjunction with our neutron scattering studies of Yb2Ge2O7 show it neutron powder diffraction data taken below TN, we selects an AFM state. Despite this difference, these find that the 3D ordered magnetic structure consists Yb pyrochlores share the same unusual spin of b-axis aligned antiferromagnetic layers (3.55μB) dynamics in zero field, which has been proposed to slightly canted in the c-axis, as well as layers of small be a result of phase competition. Further progress has antiferromagnetic c-axis aligned moments (0.72μB). been impeded by inaccessibility of single crystals of K3Er(VO4)2 provides a clear example of how pseudo- Yb2Ge2O7. We report inelastic neutron scattering spin-½ ordering can manifest as widely varying measurements on a co-aligned mosaic of single magnetic moment sizes depending on the pseudo- spin orientation, due to g-tensor anisotropy. Strontium titanate (SrTiO3, STO) is one of the most important transition metal oxides: it is a model B03.01.03 perovskite with a structural phase transition, and also Magnetic Properties of the Doped Mott Insulator one of the most commonly used single crystal YTiO3 substrates for epitaxial growth of oxide thin films. Joseph Joe1, Sajna Hameed1, Peter Gehring2, Masaaki Superconductivity in STO occurs at unusually low Matsuda3 and Martin Greven1; 1University of carrier densities at temperatures well below 1 K and Minnesota Twin Cities, United States; 2National is not understood, even five decades after its Institute of Standards and Technology, United discovery. Building on our recent work on oxide States; 3Oak Ridge National Laboratory, United superconductors [1], we have begun to explore States another interesting property of STO: its high ductility at room temperature, which has allowed us to The transition metal oxides RTiO3, where R is a plastically deform single crystals using uniaxial trivalent rare-earth ion, are typical Mott-Hubbard pressure. Using diffuse neutron and X-ray scattering, insulators, with the Ti3+ ion in the 3d1 configuration. transport and magnetometry measurements, we have The observed GdFeO3-type tilt distortion of the determined the influence of this compressive plastic TiO6 octahedra controls the electron transfer between deformation on the structural, transport and magnetic the Ti 3d1 and O 2p orbitals, and hence constitutes a properties of STO, with particular emphasis on the bandwidth-control mechanism. The end members superconducting state. The results push the limits of YTiO3 and LaTiO3 of this series exhibit large and superconductivity in low-density electronic systems small distortions, respectively, with Ti-O-Ti bond such as STO, suggest that deformed STO is a angles of 140o and 156o. The physical properties potential high-temperature superconductor and, more across the RTiO3 series exhibit significant variation broadly, demonstrate the feasibility of plastic dependent on the rare-earth ion, as YTiO3 is a deformation as a tool to manipulate the electronic ferromagnet (FM), whereas LaTiO3 is an properties of quantum materials [2]. antiferromagnet (AFM). In both cases, hole doping induces a metallic state; the insulator-metal transition [1] D. Pelc, Z. Anderson, B. Yu, C. Leighton, and M. (IMT) in Y1-xCaxTiO3 and La1-ySryTiO3 occurs at Greven, Nat. Commun. 10, 2729 (2019). wildly different concentrations of x=0.37 and y=0.05, [2] S. Hameed, D. Pelc, Z. W. Anderson, R. J. respectively [1]. The robust insulating state of Spieker, M. Lukas, Y. Liu, M. J. Krogstad, R. YTiO3 makes the system particularly interesting, Osborn, C. Leighton, and M. Greven, notwithstanding various other peculiarities, as it has arXiv:2005.00514 (2020). been argued that orbital order is responsible for the ferromagnetic ground state. Here we report elastic Funding: Work supported by the Department of and inelastic neutron scattering results for Y1- Energy through the University of Minnesota Center xLaxTiO3 and Y1-xCaxTiO3, with focus on the spin- for Quantum Materials under DE-SC-0006858. wave spectrum and magnetic order parameter, in order to elucidate the respective evolution from FM B03.01.06 to AFM insulator and FM insulator to paramagnetic Local Atomic Correlations in 1T-TaS2- metal. The work at the University of Minnesota was 2xSe2x across the CDW Phases funded by the Department of Energy through the Sharon S. Philip and Despina Louca; University of University of Minnesota Center for Quantum Virginia, United States Materials, under DE-SC-0006858. [1] M. Imada, A. Fujimori, and Y. Tokura, Rev. Mod. Studies on transition metal dichalcogenides (TMD) is Phys. 70, 1039 (1998) of great significance due to their interesting topological properties and unusual superconductivity. B03.01.04 These materials are prototypical examples of charge Influence of Plastic Deformation on the density wave (CDW) instability where the CDW state Structural, Transport and Magnetic Properties of is in close proximity to superconductivity. In this Strontium Titanate project, we investigate the CDW phases in TaX2 class 1 1 Sajna Hameed , Damjan Pelc , Zachary W. of TMDs, where X = S, Se. 1T-TaS2 has attracted Anderson1, Richard J. Spieker1, Marin Lukas2, much attention recently because of the possibility of Yaohua Liu3, Matthew J. Krogstad4, Raymond an exotic quantum spin liquid (QSL) state. This is Osborn4, Chris Leighton1 and Martin proposed to be one of the few model spin Greven1; 1University of Minnesota Twin Cities, configurations that may harbor a QSL state. 1T- 2 3 United States; University of Zagreb, Croatia; Oak TaS2 undergoes a series of phase transitions upon Ridge National Laboratory, United States; 4Argonne cooling and achieves a commensurate CDW National Laboratory, United States (CCDW) phase below 183K. The CCDW transition is accompanied by a periodic lattice distortion. It is reported that the system forms a √13×√13 super cell, the Cu-O bond stretching branch, suggesting that described as a star-of-David, with a large distortion using the correct insulating electronic structure is of about 10% of the lattice constant, in the CCDW necessary for accurate first-principles modelling of state. Simultaneously, electron correlation effects set phonons in the cuprates. *This work was supported in and localize the unpaired electron at the center of by the DOE, Office of Basic Energy Sciences, Office star, leading to a Mott insulating state with S = 1/2 of Science, under Contract No. DE-SC0006939. spins arranged in an ideal triangular lattice of 1T- TaS2. On the other hand, 1T-TaSe2 undergoes CCDW B03.01.08 transition at a higher temperature of 473 K and Anomalous Magnetic Structure and Dynamics in remains metallic upon cooling to low temperatures. FeGe2 No metal-to-insulator transition is observed in 1T- Yaokun Su1, Hillary Smith2, Matthew Stone3, 3 1 1 TaSe2 which implies that the spin on the unpaired Douglas L. Abernathy and Chen Li ; University of electron is not localized within the star-of-David and California, Riverside, United States; 2California suggests a different distortion is at play. This is Institute of Technology, United States; 3Oak Ridge interesting given that both 1T-TaS2 and TaSe2 have National Laboratory, United States trigonal symmetry and undergo similar periodic modulations on CCDW transition. To elucidate the Inelastic neutron scattering was used to probe order nature of the local atomic correlations upon cooling and dynamics in single crystal FeGe2 at 20 and 300 into the CCDW transition and understand the origin K. An unusual magnetic feature in the dynamical of the differences in TaS2 and TaSe2, the local atomic structure factor was found in the HK0 planes. It was structure was obtained by Fourier transforming the found that the anomaly only exists as the dynamic synchrotron X-ray diffraction data. In this project, we magnetic structure at low temperature, but part of it investigate the local structure and ordering in 1T- condenses to the static structure at room temperature. TaS2 and 1T-TaSe2 systems as they undergo the CDW At 300 K, the magnetic anomaly appears to be rods transition by analyzing the atomic pair distribution intensity connecting magnetic zone centers along function (PDF). We also look at low-energy inelastic [110] and [1-10]. At 20 K, the rods intensity is neutron scattering measurements to study magnetic detached from the magnetic zone centers to form a excitations in this material. dot-dash-dot pattern. This anomaly is far from the magnetic satellites of the incommensurate state. The B03.01.07 large discrepancies between experiment and First Principles Study of the Phonons in an phonon/magnon calculation are attributed to the Undoped Insulating Cuprate strong magnon-phonon interactions and it is Tyler C. Sterling and Dmitry Reznik; University of speculated that they may also be related to the Colorado Boulder, United States anomaly.

Accurate first-principles modelling of the cuprates is essential to interpreting the results of experiments. However, most previous calculations performed at SESSION B03.02: Nanomaterials and low doping find a metallic ground state instead of the experimentally determined insulating state. The Layered Thin-Film consequences of this failure are particularly apparent when comparing phonons calculated from the metallic electronic structure to inelastic neutron and X-ray data. Measurements of the Cu-O branch in B03.02.01 La2CuO4 (LCO) at low doping show very little Using a Combination of Neutron and X-Ray dispersion across the Brillouin zone, while first Reflectometry to Reveal Complex principles density functional theory (DFT) Antiferromagnetic Canting Structures in Oxide calculations show this branch dispersing steeply Heterostructures (which actually agrees better with the overdoped metallic state). However, a recently developed DFT Ingrid Hallsteinsen1,2, Kristoffer Kjærnes1, Alexander exchange-correlation functional has been shown to J. Grutter3, Padraic Shafer2 and Elke accurately predict the insulating electronic structure Arenholz2; 1Norwegian University of Science and of LCO. In my talk, I will present the results of Technology, Norway; 2Lawrence Berkeley National phonon calculations performed using this new Laboratory, United States; 3National Institute of functional and demonstrate how DFT results can be Standards and Technology, United States directly compared to data from inelastic neutron and X-ray experiments. In the case of undoped LCO, we Interface functionality in oxide heterostructures can find better agreement than previously reported be controlled by strain engineering, due to the nearly between the calculated and measured dispersion of degenerate ground states of competing order in these systems. A central question is what role structural full neutron spin polarization analysis involving a reconstructions play inestablishing and controlling super mirror, RF flipper, and He3 spin analyzer. This new magnetic spin textures. In general, probing probes the Q-range of 0.0003 to 0.13 inverse antiferromagnetic spin structures is difficult but angstroms. Spin-flip scattering indicates that while important in new spintronic devices. To address this the magnetism at 0.007 T nearly follows the question, (111)-oriented epitaxial heterostructures of structural scattering for most of the observable Q- antiferromagnetic (AF) LaFeO3 (LFO) and range, but at very low Q below about 0.001 inverse ferromagnetic La0.7Sr0.3MnO3 (LSMO) is used as angstroms the magnetic scattering diverges front the model system, and we present data on the interplay structural scattering and quickly drops toward zero between AF spin axis of LFO and the occurrence of intensity, indicative of anti-ferromagnetic alignment magnetic reconstructions at the (111)-oriented between magnetic domains within grains (both LSMO/LFO interface. To probe the spin texture of samples). Additionally, the difference between DD the different layers, we rely on a combination of soft and UU scattering (or between D and U for half- x-ray spectroscopy, x-ray photoemission electron polarization without the He3 spin analyzer) microscopy and neutron reflectometry. The AF LFO effectively probes the nuclear-magnetic cross-term. is spin-flopped coupled (perpendicular) to the FM We see an oscillatory negative and positive LSMO, however at the interface a canting of the AF difference which indicates that the net magnetism spins is induced, resulting in a net moment in the parallel to the applied magnetic field is not coherent LFO and a spiral spin structure. We show that the AF with the underlying structure for both magnetic field spin axis in single layers of LFO can be tuned by conditions. This difference is larger in magnitude and thickness, crystallographic orientation and strain. with a different Q-dependence for the higher field Hence, we can by using different substrates induce (more detailed modeling in progress). For both different types of spiral structures at the interface. We samples (180 nm and 550 nm samples) conventional use soft x-ray resonant reflectivity with linear SANS does not reach a sufficiently low Q to observe polarized light and spin polarized neutron reflectivity the magnetic morphologies described; the to directly probe the depth dependence on the AF and polarization analysis is additionally needed no FM spin axis in these systems. In addition, we can observe the magnetic structure that is dominated by use magnetic fields to change the spiral structure. the structural scattering contribution. Due to the magnetic exchange coupling at the interface, the AF spin axis turns/rotates when an [1] K. Dey, S. Majumdar, and S. Giri, Phys. Rev. applied field aligns the FM spins. Hence, creating B 90, 184424 (2014). systems with a competition between exchange [2] G. Lin, Y. Wang, X. Luo, J. Ma, H. Zhuang, D. coupling and magneto crystalline anisotropy enables Qian, L. Yin, F. Chen, J. Yan, R. Zhang, and others, us to control the spin canting in the AF layer. Phys. Rev. B 97, 064405 (2018). [3] N. Mufti, G. Blake, and T. Palstra, J. Magn. B03.02.02 Magn. Mater. 321, 1767 (2009). Probing Room Temperature Magnetism in Nano- MnCr2O4 Spinels Using Polarization-Analyzed Access to vSANS was provided by the Center for vSANS High Resolution Neutron Scattering, a partnership Kathryn L. Krycka1, Hector C. Mandujano2, Eduardo between the National Institute of Standards and Martinez-Teran2, Ahmed El-Gendy2 and Technology and the National Science Foundation Harikrishnan S. Nair2; 1National Institute of under Agreement No. DMR-1508249. HSN and AEG Standards and Technology, United States; 2The acknowledge Rising Stars award from UT and UTEP University of Texas at El Paso, United States start-up funds.

The spinel chromate MnCr2O4 is conventionally B03.02.03 interesting in that it is magnetoelastic and magneto- Strain vs Charge Mediated Magnetoelectric dielectric below TN = 43 K and shows ferroelectricity Coupling across the Magnetic Oxide/Ferroelectric at TS = 18 K with the onset of short-range spiral spin Interfaces order [1, 2, 3]. However, high temperature magnetic Edwin Fohtung1, Binod Paudel2, Igor Vassiliev2 and susceptibility (~1000 K) of our ball-milled Valeria Lauter3; 1Rensselaer Polytechnic Institute, nanoparticles of 550 + 150 nm or 180 + 50 nm United States; 2New Mexico State University, United indicates the presence of spin correlations up to 800 States; 3Oak Ridge National Laboratory, United K. To understand the magnetic morphology at States remanence (0.007 T) and higher field (1.5 T) at 300 K, we employ the converging beam with high We utilize polarized neutron reflectometry (PNR) in resolution detector option at VSANS (the very Small consort with ab initio based density functional theory Angle Neutron Scattering instrument at the NIST (DFT) calculations to study magnetoelectric coupling Center for Neutron Research), additionally adding at the interface of a ferroelectric PbZr0.2Ti0.8O3 (PZT) and magnetic La0.67Sr0.33MnO3 (LSMO) B03.02.06 heterostructure grown on a Nb-doped SrTiO3 (001) Model for Multiferroic (NH4)2FeCl5 (H2O)* substrate. Functional device working conditions are Randy Fishman1, Jaime Fernandez-Baca1, Wei mimicked by gating the heterostructure with a Pt top Tian1 and Jan Musfeldt2; 1Oak Ridge National electrode to apply an external electric field, which Laboratory, United States; 2The University of alters the magnitude and switches the direction of the Tennessee, Knoxville, United States ferroelectric (FE) polarization, across the PZT layer. PNR results show that the gated PZT/LSMO exhibits The multiferroic behavior of any material sensitively interfacial magnetic phase modulation attributed to depends on the microscopic interactions between the ferromagnetic (FM) to A-antiferromagnetic (A-AF) spins. We evaluate the magnetic interactions in the phase transitions resulting from whole accumulation. multiferroic erythrodsiderite (NH4)2FeCl5 (H2O) by When the net FE polarization points towards the comparing inelastic neutron scattering spectra of a interface (positive), the interface doesn't undergo a single crystal sample with a simple Heisenberg model magnetic phase transition and retains its global FM containing five exchange interactions and an easy- ordered state. In addition to changes in the interfacial plane anisotropy. The cycloidal spin state in magnetic ordering, the global magnetization of every bc plane is produced by two competing LSMO increases while switching the polarization exchange interactions. Using the observed from positive to negative and decreases vice versa. wavevector of this cycloidal spin state as a constraint, DFT calculations indicate that this enhanced excellent agreement is found between the observed magnetization also correlates with an out of plane and predicted spectra. The exchange and anisotropy tensile strain, whereas the suppressed magnetization parameters also provide excellent agreement with for positive polarization is attributed to out of plane inelastic neutron-scattering spectra in the high-field compressive strain. These calculations also show the spin-flop phase. The resulting exchange and coexistence of FM and A-AF phases at zero out of anisotropy parameters are compared with the plane strain. Charge modulations throughout the predictions of first-principle calculations. LSMO layer appear to be unaffected by strain, *Work supported by the US Department of Energy, suggesting that these charge mediated effects do not Office of Science, Office of Basic Energy Sciences, significantly change the global magnetization. Our Materials Sciences and Engineering Division PNR results and DFT calculations are in consort to verify that the interfacial magnetic modulations are due to co-action of strain and charge mediated effects with the strain and charge effects dominant at SESSION B04.01: Thermal different length scale. Properties and Phonons B03.02.05 Magnetoelectric Coupling and Magnetic Structure of RbFe(SO4)2 Junjie Yang; New Jersey Institute of Technology, B04.01.01* United States Negative Thermal Expansion and Entropic Elasticity in ScF3 Type Empty Perovskites 1 2 1 Multiferroics that simultaneously exhibit ferroelectric Igor Zaliznyak , David Wendt , Emil Bozin , Joerg 3 3 4 and magnetic orders have attracted much attention C. Neuefeind , Katharine Page , Brent Fultz and 1 1 due to their intriguing physics, such as the nature of Alexei Tkachenko ; Brookhaven National 2 the competing magnetic interactions and their Laboratory, United States; Stanford University, 3 coupling to the lattice degree of freedom. Recently, United States; Oak Ridge National Laboratory, 4 we synthesized single crystals of a new multiferroic United States; California Institute of Technology, material RbFe(SO4)2 (RFSO). RFSO exhibits an United States antiferromagnetic transition near 4 K which is associate with the onset of multiferroelectrcity. The While most solids expand when heated, some electric polarization as a function of magnetic field materials show the opposite behavior: negative suggests a strong magnetoelecric (ME) coupling thermal expansion (NTE). NTE is common in effect in RFSO below 4 K. We also study the polymers and biomolecules, where it stems from the magnetic structures of RFSO by neutron scattering entropic elasticity of an ideal, freely-jointed chain. technique. In this work, we will discuss the ME The origin of NTE in solids had been widely believed coupling effect, the phase diagram and magnetic to be different, with phonon anharmonicity and structures of RFSO single crystal. specific lattice vibrations that preserve geometry of the coordination polyhedra – rigid unit motions (RUMs) – as leading contenders for explaining NTE. Our neutron scattering study of a simple cubic NTE material, ScF3, overturns this consensus [1]. We owing to a surprising cancellation of errors. On the observe that the correlation in the positions of the other hand, the experimental thermal expansion of neighboring fluorine atoms rapidly fades on NaBr [4] is four times larger than predicted with the warming, indicating an uncorrelated thermal motion, QHA. A single crystal of rocksalt NaBr was which is only constrained by the rigid Sc-F bonds. measured on ARCS at the SNS with 201 rotations in These experimental findings lead us to a quantitative, half-degree increments about its [001] axis. Data quasi-harmonic theory of NTE in terms of entropic reduction included a new iterative correction for the elasticity of a Coulomb floppy network crystal, multiphonon background from a two-atom crystal, which is applicable to a broad range of open and gave the 4D scattering functions S(Q,E). After framework solids featuring floppy network using Bragg diffractions to assess nonlinearities from architecture [2]. The theory is in remarkable the ARCS detector array, the higher Brillouin zones agreement with experimental results in ScF3, were folded back into an irreducible wedge in the accurately describing NTE, phonon frequencies, first zone to obtain spectral intensities of the phonon entropic compressibility, and structural phase dispersions. These INS measurements reveal an transition governed by entropic stabilization of unqualified failure of the QHA to predict the criticality. We thus find that NTE in a family of temperature dependence of phonon frequencies in insulating ceramics stems from the same simple and NaBr, even between 10 and 300 K. The changes in intuitive physics of entropic elasticity of an under- experimental phonon dispersions were in excellent constrained floppy network that has long been agreement with anharmonic theory, using ab appreciated in soft matter and polymer science, but initio DFT calculations (VASP with s-TDEP [3,5]). broadly missed by the “hard” condensed matter The frequencies of longitudinal-optical (LO) phonon community. Our results reveal the formidable modes of NaBr decrease significantly with universality of the NTE phenomenon across soft and temperature owing to the real part of the phonon self- hard matter [1,2]. energy from cubic anharmonicity [6]. The thermal broadening in frequency of optical modes was nearly [1] D. Wendt, et al., Sci. Adv. 5: eaay2748. (2019). as large as their thermal shifts in average frequency [2] A. V. Tkachenko, I. A. Zaliznyak. (thermal broadening is beyond the QHA). arXiv:1908.11643 (2019). Computation allowed us to pinpoint the origin of the large cubic anharmonicity as arising from first- B04.01.02 nearest-neighbor Na-Br bonds. Finally, we note that The Dominance of Pure Phonon Anharmonicity the temperature dependence of the elastic constants on the Thermal Expansion of NaBr should also depend on anharmonicity. Brent Fultz1, Yang Shen1, Claire N. Saunders1, Camille Bernal1, Douglas L. Abernathy2 and Michael [1] P.B. Allen, arXiv:1906.07103v2 (2019). E. Manley2; 1California Institute of Technology, [2] A. Togo and I. Tanaka, Scr. Mater. 108, 1 (2015). United States; 2Oak Ridge National Laboratory, [3] D.S. Kim, et al., Proc. Nat'l Acad. Sciences 115, United States 1992 (2018). [4] A. Rao, et al., J. Mod. Phys. 4, 208 (2013). Thermal expansion depends on the free [5] O. Hellman, et al., Phys. Rev. B 87, 104111 energy F(V,T) through its mixed second derivative (2013). ∂2F / ∂V∂T. The equilibrium volume V(T) [6] Y. Shen, et al., arXiv:1909.03150v1 (2019). optimizes F = E - TS by balancing phonon entropy S and elastic energy E. Usually S increases as B04.01.03 a material expands (S increases when phonon Paramagnon Drag, Magnetic Structure and frequencies are reduced), and E gives a penalty Dynamics in Li:MnTe against expansion. Most predictions of thermal Raphael P. Hermann; Oak Ridge National expansion use the quasiharmonic approximation Laboratory, United States (QHA), which assumes only a volume dependence of the phonon frequencies [1,2]. The QHA neglects pure MnTe is a semiconductor which undergoes anharmonicity, where phonon frequencies depend on antiferromagnetic ordering below its rather high Néel temperature at a fixed volume. Both thermal temperature of 307 K. Interestingly, MnTe presents a expansion and entropy depend on all phonons in the strong increase in thermopower at the Néel crystal, so measuring phonon dispersions by inelastic temperature, first reported reported by Wasscher and neutron scattering (INS) enables new and incisive Haas[1]. This suggests an attractive route to develop physical tests. Our recent INS study showed that the this material class for thermoelectric applications. QHA gave the wrong sign for the thermal frequency Harnessing the magnetic degree of freedom in shifts of most phonons in silicon [3], and is therefore thermoelectric materials is an elegant way to mitigate physically incorrect. Somewhat unfortunately, the the balancing act of optimizing the counteracting QHA did predict adequately the thermal expansion quantities of electronic conductivity and thermopower. The presence of excess thermopower by flatter regions – like a train of ocean waves rolling above the electronic diffusion value and the presence into shore. Nonlinear traveling waves have unique of a spin-Seebeck effect in the paramagnetic state properties that are important in many disciplines suggest that local thermal magnetic fluctuations of including optical communications, conducting the magnetization give rise to a spin-Seebeck effect polymers, biology, magnetism, and nuclear physics. similar to that encountered in ferromagnets. Yet, despite the crucial importance of crystal lattice Measurements on lightly Li-doped MnTe indicate vibrations in fundamental and applied science, that a large thermoelectric figure of merit of ZT=1 is nonlinear traveling waves have not been observed in possible at T > 800 K, making Li:MnTe the first ordinary crystals. In this talk we show that nonlinear viable thermoelectric material based on magnetism traveling waves exist in fluorite-structured thoria, driven thermopower [2]. Inelastic neutron scattering, urania, calcium fluoride, and barium fluoride using nuclear inelastic scattering, and neutron diffraction neutron scattering and first-principles calculations. reveal the lattice[3] and magnetic structure and These nonlinear waves are observed as sharp dynamics and specifically the characteristic magnetic dispersion curves at temperatures ranging from 5 K fluctuation frequency and correlation length for the up to 1200 K, extend to frequencies 30-40% higher Mn magnetic moments, which are required inputs for than the maximum phonon frequency, and travel at a microscopic model of paramagnon drag in the group velocities comparable to or higher than the paramagnetic regime. Suprisingly, the paramagnon fastest phonon. Given that these nonlinear modes are lifetime of ~30 fs is temperature independent still observed at 5 K, our measurements imply that between 307 and 900 K. the quantum zero-point motion contains propagating nonlinear modes, or entangled phonons. Prior [1] JD Wasscher and C Haas, Physics Letters 8 302- measurements at reactor-based sources did not probe 304 (1964). the high energies where these modes are found [2] Y Zheng, T Lu, Md MH Polash, M because relatively few epithermal neutrons are Rasoulianboroujeni, N Liu, ME Manley, Y Deng, PJ produced at a reactor source. Our measurements were Sun, XL Chen, RP Hermann, D Vashaee, JP made possible by the abundant epithermal neutrons Heremans, H Zhao, Paramagnon drag yields a high available at a spallation neutron source. The thermoelectric figure of merit in Li-doped MnTe, existence of these waves in three-dimensional Science Adv. 5, eaat9461, (2019). crystals may have ramifications for a wide range of [3] S Mu, RP Hermann, S Gorsse, H Zhao, ME properties. Manley, RS Fishman, L Lindsay, Phonons, magnons, and lattice thermal transport in antiferromagnetic B04.01.05 semiconductor MnTe, Physical Review Materials 3, Vibrational Entropy of Glass Transitions in 025403 (2019). Metallic and Molecular Glasses Camille Bernal1, Hillary Smith2, Claire N. Saunders1, O Garlea, D Abernathy, K Taddei, S Calder, D Stefan Lohaus1, Marios Demetriou1, Douglas L. Moseley and coauthors of Ref. [2] and [3], are Abernathy3 and Brent Fultz1; 1California Institute of gratefully acknowledged. Work supported in part by Technology, United States; 2Swarthmore College, the U.S. Department of Energy (DOE), Office of United States; 3Oak Ridge National Laboratory, Science, Basic Energy Sciences, Materials Sciences United States and Engineering Division. This research used resources at the Spallation Neutron Source (SNS), a When a glass (an amorphous solid) is heated, it DOE Office of Science User Facility operated by the softens before crystallization. This soft amorphous Oak Ridge National Laboratory (ORNL). phase is a viscous liquid that is deeply undercooled below its usual melting temperature. Significant heat B04.01.04 is adsorbed in this “glass transition”, raising the Nonlinear Propagating Modes Observed beyond entropy of the material. Different theories, based on the Phonons in Fluorite-Structured Crystals indirect experimental measurements, have attributed Michael E. Manley1, Matt Bryan1, Lyuwen Fu2, varying amounts of this entropy (of the glass Douglas L. Abernathy1 and Chris Marianetti2; 1Oak transition) to changes in vibrational entropy and Ridge National Laboratory, United States; 2Columbia changes in configurational entropy [1]. For example, University, United States the early version of the "potential energy landscape" theory of the glass transition attributes all change in The vibrational energy of crystals is known to the heat capacity to configurational entropy and does propagate in quantized sinusoidal waves called not consider vibrational entropy [2]. The controversy phonons. In the realm of nonlinear dynamics, has continued for decades. Our group recently however, nonlinear propagating waves are also approached this problem directly. Using the high flux possible in the form of cnoidal waves where wave and efficiency of ARCS, a direct geometry neutron displacements are concentrated in solitons separated spectrometer, we measured the vibrational density of states of a metallic glass as it was heated through its spintronics such as magnetoelectric random access glass transition. This was not possible previously memory. Additionally, AFM materials are good owing to the short times available before candidates for controlling thermal transport via crystallization. Data were acquired in event mode, magnetism through external stimuli. In the current allowing it to be re-binned for analysis over multiple work, temperature and field dependent inelastic ranges of temperature while preserving statistical neutron scattering experiments were performed to accuracy. What we reported in our Nature Physics investigate the magnon-phonon interactions in nickel paper in 2017 [3] was that at most 5% of the entropy (II) oxide and chromium (III) oxide. First principles of the glass transition originated from vibrational calculations were performed on antiferromagnetic, entropy. (We measured the total entropy by non-magnetic, and pseudo-paramagnetic structures to calorimetry, and we extracted vibrational entropy understand the magnon-phonon interactions. The from the vibrational density-of-states (DOS) by interactions between these excitons are found to be conventional methods.) The vibrational DOS curves complicated and might have important implications were remarkably similar for the glass, liquid, and on both the physical properties of phonon lattice crystal phases of Cu-Zr, and the differences for Cu- dynamics, spin wave, and spin dynamics. Zr-Al were also not large. Very recently, we performed similar inelastic neutron scattering measurements during the heating of two new metallic glasses, Pt57Cu23P20 and Pt60Cu20P20. SESSION B04.02: Magnetism in These are especially fragile, meaning that they quickly become fluid above the temperature of their Low-Dimensional Systems glass transitions. Their vibrational spectra are therefore expected to change more strongly at the glass transition than Cu-Zr. In addition, we will report results on the change in the vibrational B04.02.01 spectrum of deuterated ortho-terphenyl (1,2- Signatures of Coupling between Spin Waves and diphenylbenzene, C18H14) at the glass transition. Dirac Fermions in YbMnBi2 Ortho-terphenyl is one of the most fragile glasses Aashish Sapkota1, Igor Zaliznyak1, John Tranquada1, because its shear viscosity deviates so strongly from Laura Classen1,2, Cedomir Petrovic1, Aifeng Wang3, Arrhenius behavior [4]. Analysis of these data is still Matthew Stone4, Andrei T. Savici4, Ovidiu underway, but we can say that the vibrational DOS of Garlea4 and Masaaki Matsuda4; 1Brookhaven the crystalline forms of these materials is quite National Laboratory, United States; 2University of different from the amorphous, unlike the case for Cu- Minnesota, United States; 3Chongqin University, Zr. A more complete picture will be presented at the China; 4Oak Ridge National Laboratory, United meeting. States 1. Goldstein, M., J. Chem. Phys. 64, 4767 (1976). 2. Gibbs, J. H. & DiMarzio, E. A., J. Chem. Phys. 28, In Dirac materials, coupling of Dirac charge carriers 373 (1958). with magnetism can lead to novel phenomena with 3. Smith, H. L. et al., Nature Physics 13, 900–905 potential for technological applications [1, 2]. From (2017). this perspective, 112 ternary pnictogens 4. Tolle, A., Reports on Progress in Physics 64, (A,R)MnX2 (A=Ca,Sr; R=Yb,Eu; X=Bi,Sb) represent 1473–1532 (2001). an interesting family of Dirac materials, where both the magnetism and Dirac electrons coexist, thereby providing an opportunity to study the coupling B04.01.07 between Mn spins and Dirac electrons in Bi layer [2]. Magnon-Phonon Interactions in Previous studies of spin excitations in Antiferromagnetic Oxides (Sr,Ca)MnBi2 using inelastic neutron scattering (INS) 1 1,2 1 Qiyang Sun , Bin Wei , Yaokun Su , Douglas L. have found no indication of such a coupling because 3 4 4 Abernathy , Sergey Danilkin , Dehong Yu and Chen the anomalous broadening found in itinerant magnets 1,1 1 Li ; University of California, Riverside, United was absent [2]. In contrast, our recent INS 2 3 States; Beijing Institute of Technology, China; Oak measurements of spin waves on YbMnBi2 found a Ridge National Laboratory, United small and q-independent broadening in the spin 4 States; Australian Nuclear Science and Technology waves, which is consistent with the spin-Dirac Organisation, Australia fermion coupling. Theoretical calculations show that the effect of the coupling on spin excitations is Antiferromagnetic (AFM) materials attract much suppressed by a vanishing carrier density of states at interests due to their vanishing total magnetization, the Dirac point. Nevertheless, the obtained non- which allows robustness again disturbance and negligible coupling constant is still relevant for possible long mean-free-path for applications in charge transport by carriers close to the Dirac point. [1] A. Sapkota et al, Phys. Rev. B 101, (2019), from our inelastic neutron scattering (INS) study on 041111(R)[2] M. C. Rahn et al, Phys. Rev. B 95, MnBi2Te4 single crystals, where we determined the 134405 (2017). strength of the magnetic interactions and single-ion anisotropy in the AF state (TN = 24 K). By comparing B04.02.02 our INS data to the dynamic spin susceptibility Determination of the Magnetic Order in the calculated using a linear-response density functional EuIn2As2, an Axion Insulator Candidate theory, we find that magnetic interactions up to the Simon X. Riberolles1,2, Brinda Kuthanazhi1,2, Na fourth nearest-neighbor of Mn are necessary to Hyun Jo1, Adam Kaminski1,2, Paul Canfield1,2, Tom understand the observed spin wave dispersion. We Heitmann3, Dominic H. Ryan4, Feng Ye5, Benjamin also present preliminary results of the spin waves in 1,2 1,2 1 Ueland and R. J. McQueeney ; Ames Laboratory, MnSb2Te4 (TN = 19 K), which, in addition to the 2 United States; Iowa State University of Science and single branch as oberved in MnBi2Te4, contain Technology, United States; 3University of Missouri, another high energy branch due to the presence of an United States; 4McGill University, Canada; 5Oak additional magnetic sublattice formed by antisite Ridge National Laboratory, United States exchange between Mn and Sb sites. This work is supported by the U.S. Department of Energy, Office EuIn2As2 is a Zintl compound recently reported as a of Basic Energy Sciences, Division of Materials possible first example of axion insulator with Sciences and Engineering. Ames Laboratory is antiferromagnetic (AF) longrange order and operated for the U.S. Department of Energy by Iowa characteristic colossal negative magnetoresistance. It State University under Contract No. DE-AC02- thus represents a unique platform to investigate the 07CH11358. This research used resources at the physics of axion insulators and, in particular, to focus Spallation Neutron Source, a DOE Office of Science on the interplay between the AF order and the User Facility operated by the Oak Ridge National topologically protected features of the electronic Laboratory. band structure. Here, we present results from single- crystal magnetic diffraction experiments. B04.02.05 Surprisingly, our results reveal the successive Short-Range Magnetic Correlations in the stabilization of two different sets of magnetic Bragg Disordered Ferromagnetic Alloy Ni-V Close to the reflections indexed with the propagation vectors Quantum Critical Point 1 1 1 k1=(0,0,0.31) and k2=(0,0,0) below TN1=17 and Almut Schroeder , Shiva Bhattarai , Hind Adawi , 1,2 1 TN2 =15 K, respectively, despite the chemical unit Adane Gebretsadik , Jean-Guy Lussier and Kathryn cell containing only a single Eu site. The two L. Krycka3; 1Kent State University, United 2 3 magnetic structures are believed to coexist at T≤TN2 , States; Intel Corporation, United States; National and were individually determined from refinement Institute of Standards and Technology, United States analyses. We will describe both magnetic structures and discuss the influence of our results upon the We show small angle neutron scattering (SANS) current understanding of the material’s topological results of a binary alloy Ni-V that give new insight in features. the inhomogeneous destruction of a ferromagnet close to a quantum critical point. The ferromagnetic (FM) order of Ni1-xVx vanishes towards a B04.02.04 paramagnetic phase by sufficient substitution of Ni Spin Waves in the Antiferromagnetic Topological by V. The critical temperature Tc reaches zero Insulator MnBi2Te4 and MnSb2Te4 towards xc=0.116 indicating a quantum critical point. Bing Li1,2, Simon X. Riberolles1, Liqin Ke1, Elijah Previous magnetization and μSR data noticed Gordon1, Daniel M. Pajerowski3, Andreas magnetic inhomogeneities in Ni-V and in particular Kreyssig1,2, Benjamin Ueland1, J.-Q. Yan3 and R. J. found signatures of dynamic magnetic clusters close 1,2 1 McQueeney ; Ames Laboratory, United to xc, on the paramagnetic side as well as on the FM States; 2Iowa State University of Science and side [1]. We present new major results of a small Technology, United States; 3Oak Ridge National angle neutron scattering (SANS) study [2] of Laboratory, United States polycrystalline Ni-V samples collecting data at NG7SANS at NCNR, NIST and GPSANS at HFIR, MnBi2Te4 is proposed to be the first ORNL. In Ni-V samples with low Tc<50K we find antiferromagnetic (AF) topological insulator (TI). magnetic short-range correlations in the nm-scale that The natural intergrowth of magnetic and TI layers, remain at low temperatures far below Tc in the long- and the ground state tunability via a magnetic field range ordered phase [2]. The remaining fraction of provide a unique platform for studying the interplay these short-range clusters grows towards xc and between magnetism and topological electronic states, agrees well with the cluster fraction estimate from the which give rise to the quantum anomalous Hall effect magnetization and μSR data [1]. and axion electrodynamics. Here we present results [1] R. Wang, A. Gebretsadik, S. Ubaid-Kassis et al, Andrey Mishchenko5,6; 1University of Colorado, “Quantum Griffiths phase inside the ferromagnetic United States; 2Oak Ridge National Laboratory, 3 phase in Ni1-xVx”, Phys Rev Lett 118, 267202 (2017) United States; Purdue University, United [2] A. Schroeder, S. Bhattarai, A. Gebretsadik et al, States; 4Brookhaven National Laboratory, United “Magnetic correlations in the disordered States; 5RIKEN Center for Emergent Matter Science, ferromagnetic alloy Ni-V revealed with small angle Japan; 6National Research Center "Kurchatov neutron scattering”, AIP Advances 10, 015036 Institute", Russian Federation (2020) Some of us recently characterized the spectrum of Support: This research is supported by a QuantEmX dynamic charge stripes that appears in a grant from ICAM and used resources at NIST 1.67Sr0.33NiO4 (LSNO) above charge-ordering provided by the Center for High Resolution Neutron transition temperature of 240K. Here we used Scattering, a partnership between the National inelastic neutron scattering to search for phonon Institute of Standards and Technology and the anomalies in the same compound. Most phonons are National Science Foundation under Agreement No. remarkably insensitive to the transition from static to DMR-1508249, and at the High Flux Isotope dynamic stripes, but Ni-O bond-stretching modes that Reactor, which are DOE Office of Science User modulate the volume around Ni appear to be an Facilities operated by Oak Ridge National exception. These phonons show giant Laboratory. renormalization on entering the dynamic charge stripe phase with the largest effects observed for the zone boundary half-breathing and breathing modes. B04.02.06 The latter undergoes a dramatic collapse, which Mesoscale Magnetic Structure of Spinel indicates that dynamic stripe phase hosts small Ferrimagnets polarons based on the breathing distortion of the Lazar Kish1, Alexander Thaler2, Minseong Lee3, NiO6 octahedra. Thus the dynamic stripe phase of Matthew Frith4, Dalmau Reig-i-Plessis5, Alexander LSNO is characterized by coexistence of large V. Zakrzewski1, Vivian Zapf3, Adam Aczel2, Lisa polarons in the form of dynamic stripes with small DeBeer-Schemitt2 and Gregory polarons of the breathing type. We argue that MacDougall1; 1University of Illinois at Urbana- formation of small polarons sets the nickelates apart Champaign, United States; 2Oak Ridge National from cuprates where such polarons do not form and Laboratory, United States; 3Los Alamos National point out remarkable similarities between the CMR Laboratory, United States; 4Argonne National manganites and stripe-ordered nickelates. Laboratory, United States; 5University of British Columbia, Canada B04.02.08 Quasi-Two-Dimensional Magnetism and Unusual The ferrimagnetic spinels Mn3O4 and MnV2O4 are Intermediate Spin State of Tetrahedral Co4+ in known for their anomalous magnetoresponsive Ba2CoO4 behavior, including strong magnetoelastic and Qiang Zhang1,2, Guixin Cao1, Feng Ye2, Huibo Cao2, magnetodielectric coupings. When placed under Songxue Chi2, Masaaki Matsuda2, William A. mechanical stress, these materials show a real-space Shelton1, Stephen Nagler2, Alan Tennant2, Ward separation of their volumes into hundred nanometer Plummer1, R. Jin1 and Jiandi Zhang1; 1Louisiana stripe-like regions of alternating magnetization. In State University, United States; 2Oak Ridge National MnV2O4, this domain structure is also accompanied Laboratory, United States by a hitherto undiscovered superstructure modulation on a shorter lengthscale. I will show small angle Quasi-two-dimensional (2D) magnetism exists in neutron scattering data associating these features with bulk magnetic materials when the dominant magnetic known first order magnetic transitions in these interactions are intra-planar, which is commonly materials, and their control via applied magnetic ascribed to intrinsically layered crystalline structures field. I will then draw a direct connection to bulk diminishing the inter-planar coupling through spacing magnetic measurements, and demonstrate how the effects. Here, we demonstrate that the material stripe domains can lead to anomalous magnetization Ba2CoO4 exhibits quasi 2D magnetism by combining behaviors. neutron scattering and linear spin waves theory studies, although the system lacks a clear 2D layered B04.02.07 stacking structure and displays comparable nearest- Giant Electron-Phonon Coupling of the Breathing neighbor Co-Co distances. Instead, the reduced quasi Plane Oxygen Phonons in the Dynamic Stripe 2D magnetism as revealed from the anisotropic spin Phase of La1.67Sr0.33NiO4 wave dispersions and magnetic exchange constants is Adrian Merritt1, Dmitry Reznik1,1, Andrew D. ascribed to a very weak magnetic coupling between Christianson2, Arnab Banerjee2,3, Gu Genda4 and two inequivalent quasi-2D Co layers and interpreted in terms of a frustrated network of super- disordered, nearly ferromagnetic state with a superexchange pathways Co-O--O-Co where the magnetization and susceptibility that are sensitive to overlap of the O 2p-orbital tails provides the long- the application of small fields. Small angle neutron range exchange mechanism. Furthermore, the ordered scattering and Lorentz Force Transmission Electron moment, relatively large spin gap and spin-lattice Microscopy measurements confirm these conclusions coupling may indicate a very rare intermediate spin and reveal chiral domain walls that change character state of tetrahedral Co4+ as the ground state in with thickness. For achiral ScFeGe, we find a Ba2CoO4. Our study might reshape the fundamental helimagnetic phase with a period that closely matches understanding on the quasi-2D magnetism and a conspicuous nesting of Fermi surface sheets and provide a new insight on the interplay between discover a higher entropy, glass-like, magnetic state coordinate polyhedron, spin exchange interaction, at high fields. and spin states in Cobaltites.

B04.03.02 Controlling Long-Range Skyrmion Lattices Using SESSION B04.03: Skyrmions and Field and Temperature in Fe/Gd Multilayers Unconventional Magnets Lisa DeBeer-Schemitt1, Ryan Desautels2, Nan Tang3, Sergio Montoya4,5, W.L.N.C Liyanage3, Sheena Patel5,5, Michael Fitzsimmons1,3, Eric Fullerton5, Julie A. Borchers6 and Dustin Gilbert3; 1Oak Ridge B04.03.01* National Laboratory, United States; 2Seagate Helimagnetism and Chiral Domain Walls in Technology, United Kingdom; 3The University of Hexagonal Magnets Tennessee, Knoxville, United States; 4Naval Information Warfare Systems Command, United John F. DiTusa1, Sunil K. Karna1, Madalynn States; 5University of California, San Diego, United Marshall1, W. Xie1, Lisa DeBeer-Schemitt2, David P. States; 6National Institute of Standards and Young1, Ilya Vekhter1, William A. Shelton1, Andras Technology, United States Kovacs3, Jessica K. Hebert4, W. A. Phelan5, Yan Wu2, Huibo Cao2 and Damien Tristant1; 1Louisiana Ordered magnetic skyrmion lattices presents a lush State University, United States; 2Oak Ridge National playground of new and interesting physics to explore. Laboratory, United States; 3Forschungszentrum This opportunity is provided, in part, due to the Jülich, Germany; 4Los Alamos National Laboratory, topological nature of the skyrmion. Currently, a United States; 5Johns Hopkins University, United significant effort is being made to realize skyrmion- States driven devices. These efforts are focused on designing and developing materials that can support Magnetism in non-centrosymmetric (NCS) and chiral skyrmions under ambient conditions. We have structured materials is interesting, in part, because of recently fabricated thin-films of amorphous Fe and the importance of an antisymmetric interaction Gd multilayers that support skyrmions and skyrmion caused by spin-orbit coupling known as the lattices at room temperature and zero applied Dzyaloshinskii-Moriya interaction (DMI). The magnetic field. These skyrmions are stabilized by magnetic structures that form in these compounds are dipolar interactions, rather than the Dzyaloshinskii– largely determined by the exchange interaction along Moriya interaction (DMI). By varying the film with the DMI and the crystalline anisotropy which is thickness and alloy composition we can alter the governed by the crystal symmetry. In bulk crystalline balance of the dipole interactions relative to the materials the competition between these interactions exchange and anisotropy we control the skyrmion is the cause of long period helimagnetism and have size, pitch, and stability. Using small angle neutron been shown to be key to the formation of skyrmion, scattering (SANS), we demonstrated that once hedgehog, and magnetic soliton lattices. We have formed these dipole skyrmions are stable over a large explored how the balance of these interactions field and temperature range (including determines the magnetic structures and related positive/negative/zero magnetic field and behaviors of two hexagonal structured magnets, both temperatures between 10K and 325 K, in a single NCS with one chiral (Mn1/3NbS2) and one achiral film). Interestingly, we observe temperature and field (ScFeGe). We find that these properties depend dependent changes in the scattering vector (Q) for strongly on the (a)chiral character of the crystal peak scattering related to the skyrmion lattice structure. In Mn1/3NbS2, which is formed by spacing. We observed two effects while changing the intercalating Mn between the layers of the van der magnetic field; i). ramping the field results in a Waals compound NbS2, we observe a somewhat decrease in Q suggesting an increased skyrmion lattice, and ii). when applying an field in the opposite Spectroscopy with Electrons and Peter Grünberg direction to (i), to that used to establish the skyrmion Institute, Germany lattice we observe an increase Q before leaving the lattices stability window. The origin of this change in We have investigated the magnetic properties of scattering vector has led us to identify a key Mn1/3NbS2 formed by intercalating Mn between the requirement necessary for the range of stability that layers of hexagonal NbS2 resulting in a chiral we have observed in these amorphous thin films. structured magnet. The ac- and dc-magnetic Work at UCSD supported by DOE award No. DE- susceptibility and magnetization, Small-angle SC0003678. Neutron work was done at HFIR at Oak Neutron Scattering (SANS), and Lorentz Ridge National Laboratory supported by DOE Basic Transmission Electron Microscopy (LTEM) imaging Energy Science and NCNR at National Institute of are explored and compared to calculations and Standards and Technology supported by DOC. micromagnetic simulations. The ac susceptibility [1]. R. D. Desautels et al., Phys. Rev. Materials 3, displays temperature, field, and frequency 104406 (2019) dependencies which define a complex phase diagram below the critical temperature for magnetic B04.03.03 ordering, TC = 45 K. The magnetic structure was Hysteretic Evidence of a Topological Barrier to investigated via SANS reveals a streak of magnetic Skyrmion Lattice Formation in MnSi scattering along the c-axis near Q = 0 appearing below TC, demonstrating a disordered ferromagnetic Allan Leishman1, Raí M. Menezes2,3, Eric Bauer4, (FM) or helical spin ordering. The width of this Marc Janoschek5,4, Dirk Honecker6, Lisa DeBeer- streak is reduced and becomes more intense 7 5 2 Schemitt , Jonathan White , Milorad Milošević and near TC and is gradually suppressed by the Morten R. Eskildsen1; 1University of Notre Dame, application of H along the beam. Micromagnetic United States; 2Universiteit Antwerpen, simulations of thin lamella are in agreement with 3 Belgium; Universidade Federal de Pernambuco, LTEM images of Mn1/3NbS2 where extended FM Brazil; 4Los Alamos National Laboratory, United regions result from shape anisotropy in thin samples States; 5Paul Scherrer Institut, Switzerland; 6Institut that are separated by chiral domain walls. All of these Laue-Langevin, France; 7Oak Ridge National measurements display behavior strikingly different Laboratory, United States from isostructural Cr1/3NbS2 that results from a reduced Dzyaloshinskii-Moriya interaction in Understanding the complex dynamics of skyrmion Mn1/3NbS2. formation and destruction is key to developing new technologies which make use of them. Here we report B04.03.05 the observation of a hysteresis effect associated with Crystallographic and Magnetic Structure of forming and destroying the skyrmion lattice (SkL) in Pr2PdSi3—A Single Crystal Neutron Diffraction the chiral magnet MnSi using small angle neutron Study scattering (SANS). This effect is very small when Matthias D. Frontzek; Oak Ridge National compared to the applied field of the cryomagnet (~ 2 Laboratory, United States mT vs 200 mT), but is observable and reproducible by the added precision of a custom built solenoid The intermetallic compound series R2PdSi3 (R = rare supplementing the cryomagnet. This hysteresis effect earth metal) exhibits some interesting magnetic is due to the intrinsic topological energy barrier properties like giant magnetoresistance effect [2], associated with forming the SkL from a non- strong anisotropy in the electronic properties [1] and topological phase. We have further modeled this a generic field induced phase [3]. The magnetic phase transition with micromagnetic simulations, structures are quite complex with large magnetic unit revealing that it is energetically favorable for the SkL cells due to the delicate interplay between competing to form progressively in domains of size consistent crystal electric field effect and magnetic exchange with sample inhomogeneities. interaction [4] and the addition of geometric frustration. Recently, a Skyrmion lattice has been B04.03.04 identified in Gd2PdSi3 [5]. This result has been Non-Sinusoidal Helical Magnetic Structure in published in a renowned journal and led to a renewed Chiral Helimagnet Mn1/3NbS2 interest in the magnetic properties of this series [6-8]. Sunil K. Karna1, Madalynn Marshall1, W. Xie1, Lisa Complicating the analysis of the magnetic and DeBeer-Schemitt2, David Young1, Michalis electronic properties is the fact that the Pd/Si layers Charilaou3, Andras Kovacs4 and John F. obey site occupation rules of its ions and the stacking DiTusa1; 1Louisiana State University, United of the layers yields a crystallographic superstructure 2 States; Oak Ridge National Laboratory, United [9]. In the R2PdSi3 with heavy rare earth ions (R = States; 3University of Louisiana at Lafayette, United Gd, Tb, Dy, Ho, Er, Tm) the connection between the States; 4Ernst Ruska-Centre for Microscopy and crystallographic superstructure and the magnetic structure has been studied extensively [3]. materials were unheralded and had sparse magnetic Summarizing, the magnetic structures are structure determinations, especially on single independent of the crystallographic superstructure crystals. We present the hexagonal material when the propagation vector lies exclusively in the Cu0.82Mn1.18As, an antiferromagnet with triangular hexagonal plane (R = Gd, Ho, Er). When the spin arrangment. We also will examine the magnon propagation vector contains a non-zero c-component spectrum and anisotropy of the trilayer the crystallographic superstructure imposes a antiferromagnet Fe2As. The spin structures and modulation of either the magnetic moment value or energy scales are not intuitive in this class of the in-plane easy axis. In the latter case this leads to a materials, and more phases remain to be fully canted antiferromagnetic structure. Recently, the understood. investigations on R2PdSi3 have been extended to the light rare earths for instance the Nd2PdSi3 where a small antiferromagnetic phase coexists with the dominant ferromagnetic interactions. In our SESSION B04.04: Iron Pnictides and contribution we present a detailed neutron diffraction study on a Pr2PdSi3 single crystals [10] using the Related Materials WAND2 diffractometer at HFIR. Our study will show that in this compound the crystallographic superstructure is similar to the one observed before, but significantly simpler, leading to only two B04.04.01* crystallographic domains instead of six. The Behaviors of Iron Chalcogenide Spin Ladder compound orders antiferromagnetically at TN = BaFe2X3 (X=Se,S) under Pressure 1,2 2 3 2.17K magnetic with the magnetic moments aligned Shan Wu , Thomas Smart , Junjie Yin , Craig L. 4 4 5 along the c-axis. The magnetic propagation vector is Bll , Nicholas P. Funnell , Thomas R. Forrest , 6 6 extremely small (1/20, 1/20, 0) without the Gediminas Simutis , Rustem Khasanov , Arani 2 3 7 observation of higher order reflections. Both findings Acharya , Meng Wang , Benjamin Frandsen , 2 are indication that the ground state of the non- Raymond Jeanloz and Robert 2,1 1 Kramers Pr-ion is non-magnetic and magnetic order Birgeneau ; Lawrence Berkeley National 2 is result of perturbation through the crystallographic Laboratory, United States; University of California, 3 superstructure in this compound. Berkeley, United States; Sun Yat-Sen University, 4 [1] S. R. Saha, et al., Physica B 281-282 (2000) 116 China; ISIS Neutron and Muon facility, United 5 [2] S. Majumdar, et al., PRB 62, (2000) 14207 Kingdom; Diamond Light Source, United 6 [3] M. Frontzek, Thesis, http://nbn- Kingdom; Laboratory for Muon Spin Spectroscopy, 7 resolving.de/urn:nbn:de:bsz:14-qucosa-24779 Paul Scherrer Institute, Switzerland; Brigham Young [4] M. Frontzek, et al., JMMM 301 (2006) 398 University, United States [5] T. Kurumaji, et al., Science 365 (2019) 914 [6] L. Wang, et al., JPSJ 88 (2019) 094709 In correlated electron systems, electronic phases and [7] M. Smidman, et al., PRB 100 (2019) 134423 phase transitions can be accessed by a variety of [8] E. V. Sampathkumaran, arXiv:1910.09194V2 tuning parameters including chemical doping and [9] F. Tang, et al., PRB 84 (2011) 104105 pressure. Relevant phases and phase transitions [10] Y. Xu, et al., J. Crystal Growth 312 (2010) 1992 include metal-insulator transitions, charge density wave order, structural transitions driven by nematic B04.03.06 order, anti-ferromagnetism, and superconductivity. In Spin Structures and Dynamics in Metallic most of the iron- and copper-based superconductors, Antiferromagnets the superconducting (SC) phase appears when the Daniel Shoemaker; University of Illinois at Urbana- long range ordered magnetic phase is suppressed by Champaign, United States doping carriers, with the majority of them studied to- date exhibiting a two-dimensional square lattice Recent demonstrations have raised intriguing motif. The recent finding of a pressure-induced SC possibilities of manipulating the Neel vector of phase (Pc ~ 10 GPa, Tc ~ 24 K) in the iron antiferromagnets using non-spin-polarized currents, chalcogenide spin ladder system BaFe2X3 (X=Se,S) coupling across interfaces, and/or optical excitations. has provided a new venue for studying the A key feature of these materials is that they should connection between magnetism and exhibit antiferromagnetic ordering where the Neel superconductivity without introducing disorder by vector is degenerate--for example it points along the chemical doping. However, until recently the a or b direction in a tetragonal crystal system. I will combination of high pressures and low temperatures discuss our work on the synthesis and has limited the probes of pressure-temperature (P-T) characterization of metallic antiferromagnets with phase diagrams to mainly transport measurements. degenerate Neel vectors. Until recently, these Elucidating the magnetic and structural properties requires scattering experiments under pressure, level of structural complexity on the nanometer especially neutron scattering. Although in theory length scale. Evidence is found for considerable neutron diffraction can directly determine the disorder in the c-axis stacking of the FeSe1−xSx slabs magnetic and crystal structures across the P-T phase without observable signs of turbostratic character of diagram, the associated experimental challenges the disorder. In contrast to the related FeCh (Ch = S, make the tracking of the magnetic transition Se)-type superconductors, substantial Fe-vacancies temperature TN versus pressure difficult. This can be are present in KxFe2−ySe2−zSz, deemed detrimental for compensated in part by muon spin relaxation superconductivity when ordered. Our study suggests ($\muSR$) measurements, which are sensitive to the that the distribution of vacancies significantly magnetic order; and can provide fine control on the modifies the iron-chalcogen bond-length distribution, size of the steps in pressure and temperature. In this in agreement with observed evolution of the PDF talk, we will present three complementary signal. A crossoverlike transition is observed at a experimental probes: X-ray powder diffraction composition of z≈1, from a correlated disorder state (XRD), neutron powder diffraction (NPD) and at the selenium end to a more vacancy-ordered (VO) $\muSR$ measurements under pressure in the state closer to the sulfur end of the phase diagram. BaFe2X3; we show how XRD and $\muSR$ The S-content-dependent measures of the local techniques provide information on the magnetic and structure are found to exhibit distinct behavior on structural properties across a large region of the P- either side of this crossover, correlating well with the T phase diagram complementary to that obtained by evolution of the superconducting state to that of a NPD experiments. We will mainly focus on the magnetic semiconductor toward the z≈2 end. The BaFe2Se3 ladder system that exhibits a unique block behavior reinforces the idea of the intimate type magnetic order at P = 0. We observe a structural relationship of correlated Fe-vacancy order in the transition at Ps =3.7 GPa as well as a fully ordered local structure and the emergent electronic properties. robust block-type magnetism up to P = 6.8 GPa. We observe a gradual enhancement of TN up to Ps [1] P. Mangelis et al., Physical Review B 100, followed by a considerable reduction of TN for P>Ps. 094108 (2019) These combined measurements provide essential new information on the P-T phase diagram of BaFe2X3, Work at Brookhaven National Laboratory was thereby adding new richness to the panoply of iron- supported by the U.S. Department of Energy, Office based superconductor materials. More generally, we of Science, Office of Basic Energy Sciences (DOE- demonstrate that the use of these combined BES) under Contract No. DE-SC0012704. experimental tools provides an effective scientific Alexandros Lappas acknowledges support by the approach to tackle challenging problems of interest to U.S. Office of Naval Research Global, NICOP Grant the neutron community, especially the study of Award No. N62909-17-1-2126. This research used magnetic and structural information under extreme resources at the Spallation Neutron Source, a U.S. conditions. We also find that there is a compelling Department of Energy Office of Science User need for neutron scattering capabilities combining Facility operated by the Oak Ridge National pressures above 10 GPa and temperatures below Laboratory 77K. B04.04.03 B04.04.02 Magnetic Order Arising from Frustrated Correlated Disorder-to-Order Crossover in the Interlayer Interactions in Doped SrCo2As2 1,2 1,2 1,2 Local Structure of KxFe2−ySe2−zSz Superconductor John Wilde , Bing Li , Andreas Kreyssig , Robert J. Koch1, Panagiotis Mangelis2, Hechang Lei1, Benjamin Ueland1,2, David Vaknin1, N. S. Reinhard Neder3, Marshall McDonnell4, Mikhail Sangeetha1, Yuriy Sizyuk1,2, Wei Tian3, Santanu Feygenson4, Cedomir Petrovic3, Alexandros Pakhira1, Pinaki Das1,2, Alan I. Goldman1,2, Peter Lappas2 and Emil Bozin1; 1Brookhaven National Orth1,2, D. C. Johnston1,2 and R. J. Laboratory, United States; 2IESL FORTH, McQueeney1,2; 1Ames Laboratory, United Greece; 3University of Erlangen-Nuremberg, States; 2Iowa State University of Science and Germany; 4Oak Ridge National Laboratory, United Technology, United States; 3Oak Ridge National States Laboratory, United States

A detailed account of the local atomic structure and The Fe-based superconductors and their parent disorder at 5 K across the phase diagram of the high- compounds offer prime examples of intertwined temperature superconductor KxFe2−ySe2−zSz (0≤z≤2) structural, magnetic, and electronic ground states that is obtained from neutron total scattering and can be sensitively tuned by chemical substitution. associated atomic pair distribution function (PDF) Some of the observed ground states manifest spin and approaches [1]. Various model-independent and electronic nematic phases, magnetic frustration, and model-dependent aspects of the analysis reveal a high magnetostructural volume-collapse transitions, and the interrelationship of these phenomena with States; 2Rice University, United States superconductivity are central issues in condensed matter physics. With the exception of In the AFe2As2 (A = Ca, Sr, Ba) family of iron superconductivity, many of these phenomena extend pnictides, it is well known that the superconducting to the structurally related 122-type tetragonal cobalt electron pairing is attributed to antiferromagnetic arsenides ACo2As2 (A = Ba, Ca, Sr, Eu) including (AF) spin fluctuations. However, FM spin magnetic frustration of their square Co layers and As- fluctuations may also be important to electron pairing As hybridization-driven magnetoelastic interactions. and were recently observed in Co-substituted Among the tetragonal 122 cobalt arsenides, compounds by nuclear magnetic resonance and paramagnetic SrCo2As2 is particularly interesting neutron scattering experiments. Furthermore, because neutron-scattering measurements find electronic structure calculations and angle-resolved antiferromagnetic (AF) stripe-type spin fluctuations photoemission spectroscopy (ARPES) experiments similar to those associated with superconducting indicate that ACo2As2 is in proximity to a FM pairing in the Fe-based superconductors. In addition, instability due to the existence of a flat band near the ferromagnetic (FM) fluctuations are observed by Fermi level, although these materials remain Nuclear Magnetic Resonance. In principle, tuning the paramagnetic down to 2 K with AF low-energy spin SrCo2As2 system towards stripe-type AF order fluctuations. Since chemical substitution can shift the through appropriate chemical substitution may realize Fermi level relative to the band structure, substitution superconductivity. Here, we present a study of of Co with Ni will drive the system toward a Van Sr(Co1-xNix)2As2 [1] and (Ca1-xSrx)Co2As2 [2] single Hove singularity associated with the flat band and crystals using neutron diffraction and high-energy x- efficiently promote the FM instability. Therefore, it is ray diffraction. We find helical-AF order consisting interesting to investigate how AF and FM spin of FM-aligned transition-metal layers stacked AF fluctuations evolve in A(Co1−xNix)2As2 and to along c. We show that the details of the AF stacking explore the relevant emergent phenomena. We can be described in terms of a one-dimensional synthesized a series of Sr(Co1−xNix)2As2 single Heisenberg model where tuning nearest and next- crystals and obtained a comprehensive phase diagram nearest neighbor interlayer coupling strengths leads with respect to field, temperature, and chemical to a variety of collinear and noncollinear magnetic substitution by magnetic susceptibility and ground states. Within the context of metallic quantum magnetization measurements. Our neutron diffraction materials it is interesting that a local moment model experiments revealed a helimagnetic order with describes well the magnetism within this frustrated magnetic moments ferromagnetically aligned in the a itinerant system. Work at the Ames Laboratory was b plane and a helimagnetic wave vector of q=(0, 0, supported by the U.S. Department of Energy (DOE), 0.56) for x= 0.1. Further Co doping reduces this wave Basic Energy Sciences, Division of Materials vector and becomes (0,0,0.37) at x = 0.2. Considering Sciences and Engineering, under Contract No. DE- both SrCo2As2 and SrNi2As2 are paramagnetic AC02-07CH11358. A portion of this research used without magnetic order at low temperature, it is resources at the High Flux Isotope Reactor, a U.S. surprising that we discovered a helical magnetic DOE Office of Science User Facility operated by the order in Sr(Co0.9Ni0.1 )2As2. Further analysis of Oak Ridge National Laboratory. This research used magnetic form factor and angle-resolved resources of the Advanced Photon Source, a U.S. photoemission spectroscopy (ARPES) data shows DOE Office of Science User Facility operated for the that the helimagnetism is associated with a flat band U.S. DOE Office of Science by Argonne National of dx2-y2 orbital character. On one hand, the helical Laboratory under Contract No. DE-AC02- wave vector with a value nearly equal to (0,0,0.5) can 06CH11357. not be explained by the molecular field theory with J1 and J2 model, on the other hand, the existence of a [1] J. M. Wilde, A. Kreyssig, D. Vaknin, N. S. flat band at the Fermi level impose a serious Sangeetha, Bing Li, W. Tian, P. P. Orth, D. C. challenge on the estimation of wave vector from Johnston, B. G. Ueland, and R. J. McQueeney, Phys. Fermi surface nesting picture. We will discuss the Rev. B 100, 161113(R) (2019). possible origin of this helical magnetic order and [2] Bing Li, Y. Sizyuk, N. S. Sangeetha, J. M. Wilde, further evidence of spin fluctuations from inelastic P. Das, W. Tian, D. C. Johnston, A. I. Goldman, A. neutron scattering may help understand it. Kreyssig, P. P. Orth, R. J. McQueeney, and B. G. Ueland, Phys. Rev. B 100, 024415 (2019).

B04.04.04 Flat-Band Magnetism and Helical Magnetic Order in Ni-Doped SrCo2As2 Yu Li1, Pengcheng Dai2, John F. DiTusa1 and David P. Young1; 1Louisiana State University, United SESSION B05.01: Topological that WTe2 has only the Td phase at ambient pressure since the material was first structurally characterized Materials many decades ago. However, from the structural phase diagram of Mo1-xWxTe2, the increase of the transition temperature with W-substitution, measured up to x~0.5, suggests the possibility of a Td-1T’ B05.01.01* transition in WTe2 should be investigated. Neutron Quantum Oscillations from Networked scattering experiments at the High Flux Isotope Topological Interfaces in a Weyl Semimetal Reactor (HFIR) at Oak Ridge National Laboratory 1,2 2 2 I-Lin Liu , Colin Heikes , Taner Yildirim , Chris (ORNL) were conducted on a WTe2 single crystal. 1 1 1,2 Eckberg , Tristin Metz , Sheng Ran , William Elastic scans along (2, 0, L) indicate a Td-1T’ 2 1 Ratcliff , Johnpierre Paglione and Nicholas structural phase transition in WTe2 at ~565K. Unlike 2,1 1 Butch ; University of Maryland, United for MoTe2, the structural transition in WTe2 proceeds 2 States; National Institute of Standards and without hysteresis. No intermediate phase is present Technology, United States across the phase boundary, in contrast to the Td* Layered transition metal chalcogenides host many phase seen in MoTe2. The observation of the 1T' interesting topological electronic phases. MoTe2 has phase in WTe2 at ambient pressure adds details to the both noncentrosymmetric Td and centrosymmetric T' structural behavior of the Mo1-xWxTe2 family, and structures, associated with a Weyl semimetal and gives new insights into re-examination of theories higher-order topology. Pressure tunes the transition that lack a transition in WTe2. temperature between these structures and over a critical pressure range, freezes a mixed Td-T' matrix B05.01.03 at zero-temperature. New quantum oscillations in this Changes in Interlayer Phonons with Stacking critical pressure region indicate a totally different Variation in Mo1-xWxTe2 Fermi surface and topology from the topologically John Schneeloch, Yu Tao and Despina Louca; nontrivial Td and T' phases. In this mixed region, we University of Virginia, United States see no evidence for superlattice reflections or missing intensity in elastic neutron scattering measurements. While it could be very useful to understand how We conclude that a network of topological interfaces changes in layer stacking arise in quasi-2D materials gives rise to a new electronic structure. like MoTe2 where such changes occur with temperature, the small energy differences between B05.01.02 these structures makes such a theoretical Observation of a Td-1T’ Structural Phase understanding difficult. MoTe2 provides an especially Transition at Ambient Pressure in Weyl rich structural system for such study, having three Semimetal WTe2 ordered phases (as well as disordered stackings) 1 1 2 Yu Tao , John Schneeloch , Adam Aczel and within a thermal hysteresis loop, all of which can be 1 1 Despina Louca ; University of Virginia, United constructed, to a first approximation, by an A/B 2 States; Oak Ridge National Laboratory, United sequence of symmetry-equivalent stacking States operations. In principle, measuring the interlayer phonons may yield insights into subtle structural Layered transition metal dichalcogenides have attract differences between stackings and how certain much interest due to their fascinating electronic and stackings occur. Many low-energy Raman mechanic properties. Two of these materials, spectroscopy measurements have been done on MoTe2 and WTe2, are suggested to be Weyl systems such as MoS2 and few-layer graphene, but semimetals in the orthorhombic Td phase, and both this technique has the limitations that only phonons show a large non-saturating magnetoresistance. near the Brillouin zone center and with certain MoTe2 and WTe2 exist in bulk forms as stacks of symmetries are observable. We used inelastic neutron strongly in-plane bonded layers with weak van der scattering to measure interlayer phonons on a single Waals interlayer interaction and their properties often crystal of Mo0.94W0.06Te2 in its Td, Td*, and 1T' vary with stacking changes. For example, phases. Measurements were taken at the SPINS MoTe2 exhibits a first order structural phase instrument at the NIST Center for Neutron Research transition at 260K from a low-temperature at the National Institute of Standards and orthorhombic Td phase to a high-temperature Technology, and at CG4C at the High Flux Beam monoclinic 1T'∼ phase, with an intermediate pseudo- Reactor at Oak Ridge National Laboratory. Phonon orthorhombic Td* phase seen only upon warming. In energies were generally consistent with a linear chain contrast, the structural properties of WTe2 have not model, but softening was seen in Td* relative to Td, been studied extensively. Although a pressure- and on warming in 1T' from 320 to 600 K. Elastic induced transition to a monoclinic 1T’ phase has neutron scattering on many Mo1-xWxTe2 crystals been reported at room temperature, it is long believed reveal that the spacing between interlayer energy minima decreases with both W-substitution and The experimental determination of a material's warming. Together, these results offer hints into topological properties is a complicated task. changes in interlayer interactions, and may provide Conventionally, this task is fulfilled by angular- insights into why the transition in MoTe2 proceeds as resolved photoemission spectroscopy (ARPES). it does. However, a few limitations exist, such as limited materials type, high technical barrier, and restricted B05.01.04 sample environment. In this talk, we discuss how Correlating Magnetic Structure and neutron scattering may be applied to study Magnetotransport in Thin Films of the Weyl topological nodal metals and topological Semimetal Eu1−xSmxTiO3 superconductors. We will present a new neutron Ryan Need1, Zach Porter2, Kaveh Ahadi3, Zhijun dynamic structure factor formula for a generic Xu4, Brian J. Kirby4, Jeffrey W. Lynn4, Susanne topological nodal semimetal based on quantum Stemmer2 and Stephen Wilson2; 1University of many-body theoretical calculations. We show that Florida, United States; 2University of California, neutron scattering is actually a suitable technique to Santa Barbara, United States; 3North Carolina State directly probe the topological features in topological University, United States; 4National Institute of nodal metals. For Weyl semimetals in particular, we Standards and Technology, United States show that locations of Weyl nodes within the Brillouin zone, the Fermi velocities of Weyl Weyl semimetals (WSMs) are an intriguing class of fermions, which are conventionally accessible quantum materials in which the bulk band structure through ARPES, and the signatures of the Adler- topology generates surface states with linear Bell-Jackiw chiral anomaly, which is inaccessible by dispersions near the Fermi energy. In the case of ARPES, can all leave hallmark signatures in neutron magnetic WSMs, an internal magnetic field breaks spectra. These effects remain valid at finite time reversal symmetry and results in electronic temperature and realistic materials. In parallel, we properties that are strongly dependent on the also introduce how the Majorana bound states in a magnetic structure. In this work, we have used a topological superconductor can be profiled using combination of neutron diffraction and reflectometry neutron scattering techniques. Our work offers a to quantify the magnetic structure of thin neutron-based avenue to probe bulk topological Eu1−xSmxTiO3 films in order to better understand materials, with the capabilities to study a broader recent magnetotransport results suggesting that this materials type with improved versatility, such as to material is a WSM and that Sm doping can drive the study topological phase transitions. Fermi level across the Weyl node. Specifically, we report on the evolution of the average and depth- B05.01.06 dependent magnetic order in thin film samples of Ideal Imperfection for Tuning Magnetic Ground biaxially strained and electron-doped EuTiO3 for States of van der Waals Quantum Materials samples across a doping range <0.1 to 7.8 Yaohua Liu, Jiaqiang Yan, Xiaoping Wang, Bryan ×1020 cm−3. Under an applied in-plane field, the G- Chakoumakos and Yan Wu; Oak Ridge National type antiferromagnetic ground state undergoes a Laboratory, United States continuous phase transition to in-plane field- polarized ferromagnetism. The critical field for Magnetic van der Waals (vdW) quantum materials ferromagnetism decreases with itinerant carriers, yet provide a fertile playground to pursuit novel device the field evolution is qualitatively similar across the concepts, such as Lego heterostructures and Moiré doping range. Unexpectedly, we observe interfacial heterostructures. At the same time, when magnetic ferromagnetism with saturated Eu moments at low vdW materials are decorated with nontrivial fields that preceeds ferromagnetic saturation topological band structures, massive Dirac gaps can throughout the bulk of the film. We bring these form and more exotic quantum states of matter may results together to paint a complete picture of the be realized, such as the axion insulator and Chern materials magnetic structure evolution with doping insulator phases that can give rise to dissipationless and field, and discuss its connections to the unusual electronics or topological magnetoelectric effects at magnetotransport that has been observed, including elevated temperatures. To utilize a magnetic vdW anisotropic magnetoresistance and the topological material as building blocks for spintronics, it is often Hall effect. of great importance to achieve a certain nonvolatile magnetic ordering state. Here we demonstrate that B05.01.05 structural imperfections can provide a simple route Giant Neutron Response in Topological Nodal toward this end. Particularly, we show that the Semimetals and Topological Superconductors interlayer coupling of a vdW material MnSb2Te4 can Mingda Li; Massachusetts Institute of Technology, be dramatically tuned from the antiferromagnetic to United States the ferromagnetic state through the unavoidable site intermixing. In MnSb2Te4, each two-dimensional (2D) layer block consists of septuple atomic layers signatures of Skyrmions, Anomolous Hall effect and and these 2D layer blocks are weakly bound to each emergent quasi-particles. The weak vdW bonding other by vdW forces. Magnetometry studies suggest means the structure can often be reduced down to the that flux-grown MnSb2Te4 crystals show either single layer limit. CrPS4 is such a 2D vdW material antiferromagnetic-like or ferromagnetic-like that is an intrinsic semiconducting magnetic, however behaviors. We have conducted single-crystal neutron has undergone only limited experimental diffraction experiments on a series of crystals and the investigations to date. Here we present a series of results have been cross-checked at three different neutron scattering measurements to uncover the single-crystal neutron diffractometers, namely, time- underlying spin behavior. The magnetic structure is of-flight diffractometers CORELLI and TOPAZ at determined and a subtle spin reorientaiton identified. SNS and a constant-wavelength diffractometer HB- Inelastic neutron measurements (INS) provide a 3A at HFIR. There is unambiguous evidence that highly constrained exchange interaction model each crystal shows one of two different magnetic Hamiltonian. This is despite the measurements being ordering wavevectors, i.e., kF = (0,0,0) or kAF = on a powder since a balance of interaction strengths (0,0,1.5). Chemical structure refinements show that leads to a sharp separation of observed magnetic the two different magnetic ground states are excitations due to a region of anomalously low correlated with subtle differences in the Mn/Sb site- intensity in the measured S(Q, ω). The results reveal intermixing. Crystals with more Mn at the Sb site the subtle role of competing interactions in 2D vdW show ferromagnetic interlayer coupling with kF = materials, which manifest in a non-trivial magnetic (0,0,0), while those with less Mn ions sitting at the Sb transition and a tunable magnetic structure with small site favors antiferromagnetic interlayer coupling applied fields. Our results in the bulk compound with kAF = (0,0,1.5). However, in both types of provide intriguing insights that can be applied to an crystals, the magnetic moment on Mn ions at the Sb understanding of the behavior of reduced layer site is aligned antiparallel to those of Mn ions at the CrPS4. Mn site. We propose a phenomenological model that the sign and the strength of the effective inter- septuple-layer coupling is sensitive to the level of the Mn/Sb site-intermixing. This work shows an SESSION B05.02: Superconductors unconventional aspect of utilizing structural imperfections in vdW quantum materials, and such and Other Materials an ideal-imperfection approach can be generalized to tune the magnetic ground state of similar vdW compounds, particularly the topological insulator candidate MnBi2Te4 that is currently under intensive B05.02.01 study. This research used resources at the Spallation Identifying and Solving Weak Magnetic Phases in Neutron Source and High Flux Isotope Reactor, a LaFeAs1-xPxO Superconductors with Neutron DOE Office of Science User Facility operated by the Powder Diffraction Oak Ridge National Laboratory, and was partially Ryan S. Stadel1,2, Stephan Rosenkranz1, Matthew J. supported by U.S. DOE, Office of Science, BES, Krogstad1, Raymond Osborn1, Dmitry Khalyavin3, MSED. Pascal Manuel3, Rafael Fernandes4, Morten

Christensen4 and Omar Chmaissem1,2; 1Argonne B05.01.07 National Lab, United States; 2Northern Illinois Magnetic Interactions in the 2D Layered van der University, United States; 3Rutherford Appleton Waals Semiconductor CrPS4 4 Stuart Calder1, Amanda Haglund2, Yaohua Liu1, Laboratory, United Kingdom; University of Daniel M. Pajerowski1, Huibo Cao1, Travis J. Minnesota, United States Williams1, Ovidiu Garlea1 and David Mandrus2; 1Oak Ridge National Laboratory, United Neutron diffraction is an invaluable tool for States; 2University of Tennessee, Knoxville, United identifying magnetic structures. For materials with States strong magnetic moments, especially if large crystals can be grown, solving a new magnetic structure is a Materials in which the interactions are confined to straightforward, if often still non-trivial endevour in two-dimensional (2D) layers offer routes to enhanced material sciences. However, for materials with many quantum behavior and potential functionality in next dynamic phases competing for electrons in narrow generation devices. Consequently, there has been regions of composition, magnetic scattering from the recent interest in the class of materials that host isolated 2D layers weakly connected by van der prevailing phase can be quite elusive. We present the Waals (vdW) bonding. These 2D vdW materials results of a series of experiments which pushed the show intriguing behavior in the bulk, including limits of some of the highest flux high-resolution neutron diffraction instruments availble and the B05.02.03 methods necessary to work within those limits to Hidden Hydrogen and a Spin-Glass to identify new magnetic phases. Neutron powder Superconducting Transition in Quasi-1D diffraction was performed on LaFeAs1-xPxO KCr3As3 superconductors on POWGEN at the SNS at ORNL Keith M. Taddei1, Liurukara Sanjeewa1, Bing-Hua as well as WISH at ISIS at RAL. We identified Lei2, Yuhao Fu2, Qiang Zheng1, David Singh2, structures on three magnetic phases, two of which Athena Sefat1 and C. R. Dela Cruz1; 1Oak Ridge were unreported in literature and had magnetic National Laboratory, United States; 2University of moments less than 0.2 μB. By combining neutron Missouri, United States diffraction for structural analysis with muon spin resonance on EMU at ISIS at RAL for temperature In the race to find topological materials, dependence, we completed a detailed phase diagram superconductivity has found renewed interest as a including the newly discovered structures. potential host of Majorana Fermions. However, realizing such states is non-trivial requiring for B05.02.02 instance Cooper pairs with finite orbital-momentum Magnetic Structures in the Vicinity of the or Dirac-like dispersions in the normal state. Pressure-Induced Superconducting Phase in Recently, a new family of quasi-1D CeNiC2 superconductors A1,2Cr3As3 (A= Alkali metal) was Depei Zhang1, Jun Gouchi2, Feng Ye1, Takahiro discovered which is interesting in these regards for Matsuoka3, Toru Shigeoka4, Yoshiya Uwatoko2 and realizing spin-triplet superconductivity and having 1 1 Masaaki Matsuda ; Oak Ridge National Laboratory, Dirac-like crossings near EF. However, its study has United States; 2The University of Tokyo, Japan; 3The been hampered due to extreme air sensitivity and an University of Tennessee, Knoxville, United inability to charge dope. Here, we report results of 4 States; Yamaguchi University, Japan diffraction studies and DFT work on KCr3As3 which solve both these problems. We show that the reported Recently, the non-centrosymmetric ternary lanthanide growth technique inherently intercalates H into the nickel carbide, CeNiC2, was reported to show quasi-1D CrAs tubes and that the H acts as an multiple magnetic phase transitions below 20 K[1]. electron donor. Furthermore, we reveal that the Most importantly, this compound exhibits heavy- reported discrepancy in sample behavior (with some fermion superconductivity below 3.5 K under high superconducting and others spin-glasses) is actually pressure [2]. However, the magnetic structures of due to the amount of H. This work suggests a new CeNiC2 have not been well studied. In order to stoichiometry KH1-xCr3As3, which is air stable and understand the superconducting pairing mechanism, provides a charge doping mechanism. This allows for it is important to characterize the magnetic structure tuning between frustrated magnetism and in the vicinity of the superconducting phase. This talk superconductivity in a quasi-1D material as well as a will focus on the high-pressure neutron diffraction potential route to reach the predicted Dirac points. study of the magnetic structures of CeNiC2. An incommensurate antiferromagnetic phase is observed B05.02.04 in a wide pressure range from ambient pressure to the Ground State Magnetic Structure of Mn3Ge pressure where superconducting phase is induced. Jian Rui Soh1, Fernando de Juan2, Navid Qureshi3, The magnetic structures identified from both Henrik Jacobsen4, H.-Y. Wang5, Y.-F. Guo5 and polarized and unpolarized elastic neutron scattering Andrew Boothroyd4; 1EPFL, Switzerland; 2Donostia measurements and their connections to the International Physics Center, Spain; 3Institut Laue- superconductivity will be discussed in detail. Langevin, France; 4University of Oxford, United Kingdom; 5ShanghaiTech University, China [1] Motoya, Kiyoichiro, et al. "Magnetic property of CeNiC2 studied by macroscopic and microscopic We have used spherical neutron polarimetry to measurements." Journal of the Physical Society of investigate the magnetic structure of the Mn spins in Japan 66.4 (1997): 1124-1129. the hexagonal semimetal Mn3Ge, which exhibits a [2] Katano, Susumu, et al. "Exotic superconductivity large intrinsic anomalous Hall effect. Our analysis of in noncentrosymmetric and magnetic the polarimetric data finds a strong preference for one CeNiC2 revealed under high pressure." Physical of the symmetry-allowed spin structures. We show Review B 99.10 (2019): 100501. that weak ferromagnetism is an inevitable consequence of the symmetry of the observed magnetic structure, and that sixth order anisotropy is needed to select a unique ground state. B05.02.07 Vacancy-Driven Variations in the Phonon Density B05.02.06 of States of Fast Neutron Irradiated Nuclear Synthesis and Characterization of Metastable Graphite Functional Phases of Germanium Iyad Al-Qasir1, Anne Campbell2, Gabriele Sala2, Jiao Bianca Haberl, Mary-Ellen Donnelly, Yan Wu, Lin2, Yongqiang Cheng2, Fahima Islam2, Douglas L. Matthias D. Frontzek, Jamie J. Molaison and Garrett Abernathy2 and Matthew Stone2; 1University of E. Granroth; Oak Ridge National Laboratory, United Sharjah, United Arab Emirates; 2Oak Ridge National States Laboratory, United States

This work here combines in situ high pressure Research studies into the subject of radiation damage diffraction on the WAND2 beamline of the High Flux and effects in graphite began in the early 1940’s Isotope Reactor with inelastic neutron scattering on during the development of moderated nuclear recovered samples on the ARCS beamline of the reactors. Interest in this topic is expanding because of Spallation Neutron Source for the study of functional emerging applications associated with fullerenes and metastable phases of germanium. Such metastable carbon nanostructures as well as its long-standing use phases of silicon and germanium afford the as a fission moderator. Radiation damage in graphite opportunity of useful functionality different from has been explored via several experimental standard diamond-cubic Si and Ge while allowing for techniques, such as high-resolution transmission easy integration into existing technology. They could electron microscopy, atomic force microscopy, potentially yield an Si or Ge structure with ideal band scanning tunneling microscopy, Raman spectroscopy gap characteristics for solar power conversion, and x-ray photoelectron spectroscopy. Measurements improved thin-film characteristics or – in form of a of lattice excitations offer another mechanism to hydride - even for very high temperature study radiation damage in graphite. In this work, a superconductivity. These metastable phases can be series of measurements of the scattering functions of synthesized through the application of high pressure. un-irradiated and highly irradiated samples of nuclear For example, standard Si and Ge transform to a graphite were performed at room temperature using metallic phase with the structure of white tin when the Wide Angular-Range Chopper Spectrometer at compressed to ~11 GPa. Decompression from this the Neutron Spallation Source in Oak Ridge National metallic phase results in the formation of various Laboratory. The graphite samples we examined were metastable phases that are kinetically stable at exposed to different levels of neutron doses and ambient conditions, have band gap characteristics irradiation temperatures within the core of the High different from their parent material and could thus be Flux Isotope Reactor1. A super-resolution technologically exploited. Here, we characterize the reconstruction technique2 was used to obtain the simple tetragonal structure of Ge, the so-called st12- phonon densities of states from the measured Ge by inelastic neutron scattering. Therefore, st12-Ge scattering functions. The phonon densities of states of is synthesized using double-toroidal diamond anvils many defected supercells with a different vacancy in a Paris-Edinburgh press from small pieces of a Ge and interstitial configurations were calculated using wafer. The sample is pressurized to above 15 GPa the first-principles direct method. Our measurements and kept at maximum pressure for several hours to show that the scattering functions of the irradiated ensure full conversion to the metallic phase. No samples become more diffuse with increasing pressure medium and a very slow decompression rate neutron dose and the induced damage is localized. are used to improve yield of the st12 phase. This The calculations predicted very well the variations in synthesis pathway is observed in situ on WAND2 on the irradiated graphite samples phonon densities of a representative sample. The 15 GPa applied during states and indicated that these variations are mainly synthesis represent thereby the highest pressure attributed to the formation of vacancies. applied to a sample at HFIR to date. Subsequently, the phonon density of states of such st12-Ge is 1. Campbell, A., et al., Carbon. 109, 860 (2016). determined on the ARCS spectrometer. While many 2. Islam, F. et al., Rev. Sci. Instrum. 90, 105109 studies have investigated these metastable phases and (2019). also st12-Ge by density functional theory, this is the first experimental study of its phonon density of state. Acknowledgments: The irradiation of the specimens This thus yields unique insights into its potential as was performed at the Oak Ridge National Laboratory future semiconductor material. (ORNL) and sponsored by Tokai Carbon Co., Ltd. (NFE-09-02345) with the U.S. Department of Energy. A portion of this research at ORNL’s High exchange interactions. A small and finite value of the Flux Isotope Reactor and the Spallation Neutron DM interaction at 2 K provides evidence that the Source was sponsored by the Scientific User ground state of GaV4S8 is a cycloid below the Facilities Division, Office of Basic Energy Sciences, ordering temperature in zero applied field. US Department of Energy. Oak Ridge National Laboratory is managed by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 for the U.S. Department of Energy. This material is based upon Poster Session: Hard Condensed work that was conducted by I. I. Al-Qasir while a Matter Visiting Research Fellow at the Shull Wollan Center—the University of Tennessee and Oak Ridge National Laboratory’s Joint Institute for Neutron Sciences. The DFT simulations performed using the PB.01.02 High-Performance Computing Facility (SAQR) at the Magnetic Field Induced Antiferromagnetic Cone University of Sharjah. Special thanks to Ms. Naila Structure in Multiferroic BiFeO3 Masaaki Matsuda1, Sachith Dissanayake2, Tao Perveen from the Center for Advanced Materials Hong1, Yasuko Ozaki3, Toshimitsu Ito3, Masashi Research at the University of Sharjah for helping in Tokunaga4, Xinzhi Liu5, Maciej Bartkowiak5 and simulation data manipulation. Oleksandr Prokhnenko5; 1Oak Ridge National Laboratory, United States; 2Duke University, United B05.02.08 States; 3National Institute of Advanced Industrial Spin Excitations in Multiferroic Skyrmion Host Science and Technology, Japan; 4University of 5 GaV4S8 Tokyo, Japan; Helmholtz-Zentrum Berlin für Ganesh Pokharel1, Andrew D. Christianson2, David Materialien und Energie, Germany Mandrus3, Hasitha Suria Arachchige1, Matthew Stone2, Georg Ehlers2, Seunghwan Do2, Mark L. Neutron diffraction measurements were performed Lumsden2, Cristian Batista1, Hao Zhang1, Yiming under high magnetic fields up to 17 T in a Qiu4, Jose A. Rodriguez-Rivera4 and Randy multiferroic BiFeO3, in which an intermediate Fishman2; 1The University of Tennessee, United magnetic (IM) phase has been found between the cycloid and canted antiferromagnetic phases [1]. We States; 2Oak Ridge National Laboratory, United clearly found that the incommensurate magnetic States; 3The University of Tennessee, Knoxville, 4 peaks, which split perpendicular to the magnetic field United States; National Institute of Standards and in the cycloid phase, rotate by 90 degrees to align Technology, United States parallel to the field in the IM phase. The magnetic structure in the IM phase can be best described by an In the lacunar spinel GaV4S8, the interplay of spin, antiferromagnetic cone (AF-cone) structure. The charge, and orbital degrees of freedom results in a transition from the cycloid to AF-cone is the first complex phase diagram that includes ferroelectric, order and the direction of the magnetic wave vector orbitally ordered and Néel type skyrmion phases. and the easy plane of the cycloidal component are GaV4S8 exhibits a cycloidal state at zero field and a rotated by 90 degrees without changing the cycloidal Néel type skyrmion spin structure with the modulation period, whereas the transition from the application of field below 12.7 K. To understand the AF-cone to canted antiferromagnetic phase is gradual and the cone angle becomes smaller gradually physics driving the formation of these novel phases, without changing the modulation period. we have carried out inelastic neutron scattering Interestingly, the cycloidal component as well as the measurements on GaV4S8 above and below the cone angle in the IM phase shows a large hysteresis ordering temperature of 12.7 K. Dispersive spin between the field increasing and decreasing excitations with a zone boundary energy near 5.7 processes. This result, combined with the meV are observed along the [100], and [110] magnetostriction with a large hysteresis previously directions within the magnetically ordered phase. reported in the IM phase, suggests a strong Using Heisenberg model with near neighbor magnetoelastic coupling. exchange couplings and Dzyaloshinskii-Moria (DM) [1] S. Kawachi et al., Phys. Rev. Materials 1, 024408 interactions, the excitation spectra are simulated. (2017). Simulation shows ferromagnetic inter-tetrahedral couplings with J= -0.76(3) meV along x, y and - 0.60(3) meV along z-direction. It is also observed that the DM interactions are around an order of magnitude weaker than the nearest neighbor PB.01.03 signal at zero field. Inelastic neutron scattering was Lessons from La1.67Sr0.33NiO4 on Decoupled Spin used to study the magnetic excitations. The L- Excitations within Charge Stripes modulated stripe-like excitations which appear John Tranquada1, Gu Genda1, Adrian Merritt2, around 0.21 meV are proved to stem from Yb dimers. Dmitry Reznik2 and Ovidiu Garlea3; 1Brookhaven The magnetization results show that the magnetic National Laboratory, United States; 2University of moments of Yb ions are confined in ab-plane with the Colorado Boulder, United States; 3Oak Ridge same magnetic anisotropy and a proximate value of National Laboratory, United States saturation moment with pure YbAlO3.

It is well established that charge and spin stripe PB.01.05 orders develop in La1.67Sr0.33NiO4 on cooling. While Neutron Study on Average and Local Structure in the spin stripes develop two-dimensional order, there Se-Doped Ge2Sb2Te5 Materials are also spin degrees of freedom on the charge Zhenyang Xu, John Schneeloch and Despina Louca; stripes. Evidence of 1D spin correlations from the University of Virginia, United States charge stripes was first provided by the neutron scattering study of Boothroyd et al. [1]. We have Phase change material, Ge2Sb2Te5 (GST-225), has recently confirmed the 1D character of these been used in non-volatile electronic memories found excitations and have shown that they become in flash drives. This is because of its rapid reversible apparent at low temperature when the charge stripes phase transition between amorphous and crystalline become dominantly Ni-centered [2]. The decoupling phases accompanied by a very large change in the of the spins on the charge stripes from the electric resistivity and optical reflectivity. In GST- surrounding spins is due to the antiphase character of 225, the amorphous phase only appears in thin film the spin stripe order, which causes the interaction to form because a rapid cooling rate (~106K/s) is be geometrically frustrated. This effect provides an required to quench the system to the amorphous state. important lesson for stripe order in cuprates such as However, by doping with Se as in Ge2Sb2Se5xTe5- La1.875Ba0.125CuO4 [3], and how to interpret the 5x (GSST-225, 0

Breathing Pyrochlore materials have emerged as a Geometrically frustrated magnets are considered one promising candidate to study frustrated magnetism of the most interesting topics in condensed matter and topological magnons. We have initiated the physics due to a variety of exciting physics such as design and synthesis of rare-earth based Breathing quantum spin liquid, spin glass and spin ordered Pyrochlore compounds. Further, we have been using state. Rare-earth based borate family having two neutron diffraction and inelastic neutron scattering dimensional (2D) triangular lattice structure is a good techniques to probe the static and dynamic properties candidate to host many exotic ground states. We have of these compounds. In this talk, we are going to successfully synthesized and grown the centimetric present our latest experimental results for the Tm- size single crystals of a series of borate compounds based breathing pyrochlore compound with different rare earth elements. Low temperature Ba3Tm2Zn5O11. static properties of rare-earth based borates are performed using neutron diffraction while crystalline PB.01.25 electric field levels are identified using inelastic Field Dependent Neutron Scattering Studies of neutron scattering technique. In this talk, I will Breathing Pyrochlore Ba3Yb2Zn5O11 present our latest results achieved from the synthesis Sachith Dissanayake1, William M. Steinhardt1, and advanced characterization experiments. Zhenzhong Shi1, Stephen Kuhn1, Jeff Rau2, Nicholas Butch3, Matthias D. Frontzek4, Andrey Podlesnyak4, PB.01.27 Yiming Qiu3, Wangchun Chen3, David Graf5, Tao Anharmonic Effects on Phonon Eigenvectors 4 1 6 Hong , Casey Marjerrison , Michel Gingras and Sara and S(Q,E) in Quantum Paraelectric SrTiO3 Haravifard1,1; 1Duke University, United Xing He1, Dipanshu Bansal2, Barry Winn3, Songxue States; 2University of Windsor, Canada; 3National Chi3, Lynn Boatner3 and Olivier Delaire1; 1Duke Institute of Standards and Technology, United University, United States; 2Indian Institute of States; 4Oak Ridge National Laboratory, United Technology Bombay, India; 3Oak Ridge National States; 5National High Magnetic Field Laboratory Laboratory, United States and Department of Physics, Florida State University, United States; 6University of Waterloo, Canada The quantum paraelectric behavior and strongly anharmonic lattice dynamics of SrTiO3 have attracted Breathing pyrochlore systems are composed of interest for decades. Reflecting the incipient corner-sharing tetrahedra of different sizes pointing ferroelectric instability near the quantum critical in opposing directions, leading to different intra- and point and anharmonic couplings between acoustic inter-tetrahedra exchange interactions and the and optic phonons, anomalous temperature- emergence of the Dzyaloshinskii-Moriya interaction dependent phonon intensities were observed in due to loss of inversion symmetry. They are predicted multiple Brillouin zones (BZs) from inelastic neutron to host exotic physics including quantum spin ice, scattering (INS) experiments on SrTiO3. The Hybrid quantum spin liquid, and field-tunable topological Spectrometer (HYSPEC) and HB3 triple-axis magnons. Here we will present single-crystal field- spectrometer at Oak Ridge National Laboratory dependent unpolarized and polarized inelastic (ORNL) were used to track phonon intensities over a neutron scattering measurements on Yb-based wide temperature range and for a large volume in breathing pyrochlore system, as well as a theoretical reciprocal space. The S(Q,E) data reveal a strong model that can effectively describe some of our softening of the zone-center transverse optic (TO) experimental findings. mode, congruent with incipient ferroelectricity (FE), and simultaneously a strongly anomalous evolution of the intensity of transverse acoustic (TA) modes, which decreases dramatically on cooling. The experimentally observed trends are confirmed and rationalized using ab initio molecular dynamics (AIMD) and anharmonically renormalized phonon PB.01.29 methods, which achieve quantitative agreement with Neutron Scattering Studies of Yb-Based the INS experiments. By analyzing the simulated Triangular Borate temperature-dependent force-constants (FC) and Matthew Ennis1, Sachith Dissanayake1, Rabindranath eigenvectors, it is found that the structure factors Bag1, Zhenzhong Shi1, Alexander I. Kolesnikov2, |F|2 of TA and TO modes change dramatically with Jose A. Rodriguez-Rivera3, Nicholas Butch3, Hui temperature, as a direct consequence of the strong Wu3, Craig M. Brown3 and Sara Haravifard1,1; 1Duke anharmonicity in this system. Moreover, we identify University, United States; 2Oak Ridge National that the changes of Ti and O eigenvectors are Laboratory, United States; 3National Institute of responsible for these striking observations, which Standards and Technology, United States originates from Ti-O inter-atomic FC changing with temperature. These results establish how Recently, triangular antiferromagnetic materials have temperature-dependencies of phonon intensities attracted attention because competing interactions on beyond the harmonic picture can be quantitatively the lattice can give rise to exotic phenomena, such as measured through INS mapping of S(Q, E) volumes, quantum spin liquids. We have initiated systematic providing direct insights into the behavior of phonon efforts to synthesize single crystal samples of a eigenvectors in real space, and also show how first- family of rare-earth based triangular antiferromagnet principles simulations including anharmonic effects double borates. In particular, focus has been given to can reproduce and rationalize such anharmonic one member of this family, Ba3Yb(BO3)3 (BYBO), effects [1]. This work was supported by the U.S. which features spin-½ ytterbium ions on a triangular DOE. lattice. We have conducted neutron scattering studies [1] Xing He, D. Bansal, B. Winn, S. Chi, L. Boatner, on both powder and single crystal samples of BYBO and O. Delaire, “Anharmonic Eigenvectors and to probe the static and dynamic properties of this Acoustic Phonon Disappearance in Quantum system. In this talk, we will present the results of our Paraelectric SrTiO3” Phys. Rev. Lett. 124, 145901 experimental efforts. (2020).

PB.01.28 Neutron Scattering Studies of Triangular Antiferromagnet YbZnGaO4 William M. Steinhardt1, Sachith Dissanayake1, Zhenzhong Shi1, Nicholas Butch2, David Graf3, Andrey Podlesnyak4, Yaohua Liu4, Yang Zhao2, Guangyong Xu2, Jeffrey W. Lynn2, Casey Marjerrison1 and Sara Haravifard1,1; 1Duke University, United States; 2National Institute of Standards and Technology, United States; 3National High Magnetic Field Lab, United States; 4Oak Ridge National Laboratory, United States

In the last few years YbMgGaO4 and related triangular antiferromagnets emerged as promising quantum spin liquid candidates, and subsequently their ground states have been the subject of ardent debates. Though many experimental and theoretical studies have been devoted to investigating the magnetic properties of these systems at very low temperatures, and exploring a range of possible explanations for the observed spin liquid-like phenomena, a definitive description remains elusive mainly due to chemical disorder. In this presentation we discuss neutron scattering experiments in applied magnetic fields to probe static and dynamic properties of YbZnGaO4.