DOCSLIB.ORG

Magnetism and Local Molecular Field Louis Néel

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Magnetism and Local Molecular Field Louis Néel 3 December 1971, Volume 174, Number 4013 SCIENCE: Local Molecular Field On the other hand, P. Weiss was unable to offer a satisfactory solution to the problem of the origin of the molec- ular field. It was not until 1928 that Heisenberg found a mechanism of inter- Magnetism and actions that gave a satisfactory order of magnitude. From the point of view of Local Molecular Field interest to us, it is important to note only that these were interactions with a veryshort range, predominating between Louis Neel nearest-neigh-bor atoms and negligible beyond the second or third nearest neighbors. Hence, if one considers an alloy con- Downloaded from It has been known for a long time to absolute zero, the substance exposed sisting of two species A and B of atoms that ferromagnetism is due to inter- to the action of its molecular field alone distributed at random, the surroundings actions between atomic magnetic mo- hm = nJ8 acquires a certain spontaneous of the atoms may be vastly different, ments tending to align them parallel to magnetization J8. and the approximation of a single molec- one another despite the thermal agita- In this treatment, the molecular field ular field representing the action of the http://science.sciencemag.org/ tion. In order to obtain a quantitative is considered to be a uniform field inside surroundings for all the sites must be explanation of the experimental facts, the ferromagnetic sample. In addition, very poor. The theoretical problem of Pierre Weiss postulated (1) that a in order to give a more finished character treating such interactions in a rigorous ferromagnet behaved as a pure para- to his theory, P. Weiss had been led to manner is still far from resolved, but, magnet, that is, a paramagnet with distinguish between the energetic mo- while retaining the simplicity of the carriers of independent moments, with lecular field defined on the basis of the theories based on the molecular field, a magnetization given by internal energy U by the relation one can improve them considerably by making use of what I have termed the 1 = f(H/T) (1) Hm aj (4) local molecular field. and that the effect of these interactions Weiss's hypothesis amounts to writing on June 16, 2020 was equivalent to that of an imaginary and the corrective molecular field of that the energy E, of the system of magnetic field h,,,, called the molecular the equation of state hm defined, as we atoms A and B is written in the form field, proportional to the magnetization J have stated above, by E- - n(JA + JB)2 (7) h, = nJ (2) = hin) (5) where JA and JB designate the respec- and adding to the applied field H. If H tive magnetizations of atoms A and is sufficiently low, one thus obtains the Thermodynamic reasoning shows that atoms B. Actually, since this energy is magnetization law called the Curie- these two fields are related as follows: the sum of the contributions of pairs of Weiss law: nearest neighbor atoms A-A, A-B, = - dhm11 Hill mn T dT (6) and B-B, one should rather write J CH T-e (3) This particular approach, very satisfying Ee =1^(IZAAA2 + 2nABJAJB + nlBBJB) (8) with 0 = nC. If 0 is positive, the to the mind, permits one to treat and susceptibility J/H becomes infinite when explain the energetic properties of This amounts to abandoning the notion the temperature drops below the Curie ferromagnetic substances in an elegant of a general molecular field and intro- point 0. From this temperature a down and simple manner. It has the dis- ducing local molecular fields, hA = advantage of forcing one to admit as nAA1A + nABJB and hB = nABJA + Copyright ©) 1971 by the Nobel Foundation. dogma the uniformity of the molecular nBBJB acting on atoms of A and The author is professor of physics at the Uni- species versity of Grenoble, France. This article is the field and everything that follows from it, atoms of species B, respectively. lecture he delivered in Stockholm, Sweden, in in particular, the linear character of the I first developed this approach (2) in 1970, when he received the Nobel Prize in Phys- ics, a prize which he shared with Dr. Hannes thermal variation of the reciprocal 1932 and showed that the susceptibility Alfv6n. Minor corrections and additions have of been made by the author. The article is published susceptibility above the Curie point. X an alloy containing proportions here with the permission of the Nobel Foundation Advances of the theory have certainly P and Q of atoms A and B, with Curie and will also be included in the complete volume of Les Prix Nobel en 1970 as well as in the se- been retarded by this. constants CA and CB, was written as ries Nobel Lectures (in English) published by the Elsevier Publishing Company, Amsterdam and New York. Dr. Alfv6n's lecture appeared in the T(PCA + QCB) - PQC1A CB(sIA + nBB- 2nAB) (9) X - 4 June 1971 issue of Science. T T(PnAA CA + QnBB CB) + PQCA CB(nAA nBB- nAB) 3 DECEMBER 1971 985 _b -Olr -OI K on a- W. I H Fig. 1 (left). Decomposition of a planar lattice into two oppositely magnetized sublattices. Fig. 2 (middle). Motion of an antiparallel array of atomic moments acted upon by a field H. Fig. 3 (right). Thermal variation of the reciprocal suscepti- bility of an array of randomly oriented pairs of antiparallel moments. Instead of being represented by a ments are parallel and pointing in the certain, since this field is due to the straight line, the thermal variation of same direction, can cause this state of action of the neighboring atoms. These the reciprocal susceptibility l/x was ordering. Weiss and his co-workers thermal fluctuations are fluctuations in henceforth represented by a hyperbola. soon noted that the paramagnetic prop- time, but I was thus naturally led to I applied this theory to the interpre- erties of a certain number of salts were become interested in the spatial fluc- tation of the properties of platinum- suitably interpreted by a formula of the tuations and to analyze more closely Downloaded from cobalt alloys and a little later (3) to type of Eq. 3, but with a negative con- the consequences of the elementary iron-cobalt, iron-nickel, and cobalt- stant 0, that is, with a negative molecu- law of magnetic interaction: namely, nickel alloys. lar field. How such a field could pro- the existence of a coupling energy At the time, this interpretation was duce ordering at low temperature between two nearest-neighbor atoms, not received with great approval. The cannot be visualized. equal to w - cos a, where a denotes the existence of Curie-Weiss straight lines On the other hand, the Weiss theory angle of their magnetic moments. http://science.sciencemag.org/ in the [(l/X),T] representation was a was unable to account for the properties dogma so entrenched that when the ex- of paramagnetic metals such as man- periment would give a curve, it was ganese and chromium, which had a Constant Paramagnetism preferred to resolve it into successive susceptibility approximately indepen- straight lines, each corresponding to a dent of temperature and too large to be The constant w may be negative or different magnetic state obeying the attributable to Pauli paramagnetism, positive: negative in the case of ferro- Curie-Weiss law. that is, that of electrons in an energy magnetism and positive in the case band. of the negative molecular field. In the Such was approximately the state of latter case, the recourse to the molecu- Fluctuations of the the question in 1930 when I became lar field, admissible at high temperature on June 16, 2020 Weiss Molecular Field interested in the difference between the when the situations of all the atoms two Curie points, that is, in the fact are identical on the average, is no In the primitive theory of Weiss, the that the Curie point Op deduced from longer admissible at low temperature, molecular field coefficient n and the the Curie-Weiss law, or the paramag- since the atomic magnets must then Curie point 6 both had positive values, netic Curie point, differed from the tend to become grouped in pairs of and one can understand perfectly that ferromagnetic Curie point Of, the tem- atoms with antiparallel moments. this molecular field, which has a finite perature of disappearance of spon- I thus noted (2, p. 64) that in a positive value when all the atomic mo- taneous magnetization, whereas the Weiss theory implies the equality Of = Op. To explain this difference, I used the thermal fluctuations of the mo- lecular field, whose existence appeared *~~~~~~~~~~~~ A B Fig. 4. Variation of the susceptibility of 8 0T an array of antiparallel moments as a func- 0 T tion of the magnetic field and of the direc- Fig. 5. Influence of the magnitude of Fig. 6. Thermal variation of the recipro- tion of alignment of magnetic moments the magnetic field on the susceptibility of cal susceptibility of an antiferromagnetic relative to the crystal lattice. an array of antiparallel moments. substance. 986 SCIENCE, VOL. 174 body-centered cubic lattice composed of two simple cubic interpenetrating sublattices, the stable equilibrium at low temperature corresponded to an orien- tation in a certain direction of the moments of atoms in one of the sub- lattices and to an opposite orientation of the atomic moments of the other suiblattice, as is shown in Fig. 1 in the case of a planar lattice. This array is perturbed (Fig. 2) under the action of a magnetic field and acquires an aver- age induced magnetization per atom given by I p= g2H/6pw (10)C.._X,,' , ' Fig.
Load more

Recommended publications
  • Deciphering Structural and Magnetic Disorder in the Chiral Skyrmion Host Materials Coxznymnz (X + Y + Z = 20)
    Deciphering structural and magnetic disorder in the chiral skyrmion host materials CoxZnyMnz (x + y + z = 20) Joshua D. Bocarsly,1, ∗ Colin Heikes,2 Craig M. Brown,2 Stephen D. Wilson,1 and Ram Seshadri1 1Materials Department and Materials Research Laboratory, University of California, Santa Barbara, California 93106, United States 2Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States (Dated: January 9, 2019) CoxZnyMnz (x + y + z = 20) compounds crystallizing in the chiral β-Mn crystal structure are known to host skyrmion spin textures even at elevated temperatures. As in other chiral cubic skyrmion hosts, skyrmion lattices in these materials are found at equilibrium in a small pocket just below the magnetic Curie temperature. Remarkably, CoxZnyMnz compounds have also been found to host metastable non-equilibrium skyrmion lattices in a broad temperature and field range, including down to zero-field and low temperature. This behavior is believed to be related to disorder present in the materials. Here, we use neutron and synchrotron diffraction, density functional theory calculations, and DC and AC magnetic measurements, to characterize the atomic and magnetic disorder in these materials. We demonstrate that Co has a strong site-preference for the diamondoid 8c site in the crystal structure, while Mn tends to share the geometrically frustrated 12d site with Zn, due to its ability to develop a large local moment on that site. This magnetism-driven site specificity leads to distinct magnetic behavior for the Co-rich 8c sublattice and the Mn on the 12d sublattice. The Co-rich sublattice orders at high temperatures (compositionally tunable between 210 K and 470 K) with a moment around 1 µB /atom and maintains this order to low temperature.
    [Show full text]
  • Room-Temperature Helimagnetism in Fege Thin Films S
    www.nature.com/scientificreports OPEN Room-temperature helimagnetism in FeGe thin films S. L. Zhang1, I. Stasinopoulos 2, T. Lancaster3, F. Xiao3, A. Bauer4, F. Rucker4, A. A. Baker1,5, A. I. Figueroa 5, Z. Salman 6, F. L. Pratt7, S. J. Blundell1, T. Prokscha 6, A. Suter6, J. 8 8,9 2,10 5 4 1 Received: 8 November 2016 Waizner , M. Garst , D. Grundler , G. van der Laan , C. Pfleiderer & T. Hesjedal Accepted: 14 February 2017 Chiral magnets are promising materials for the realisation of high-density and low-power spintronic Published: xx xx xxxx memory devices. For these future applications, a key requirement is the synthesis of appropriate materials in the form of thin films ordering well above room temperature. Driven by the Dzyaloshinskii- Moriya interaction, the cubic compound FeGe exhibits helimagnetism with a relatively high transition temperature of 278 K in bulk crystals. We demonstrate that this temperature can be enhanced significantly in thin films. Using x-ray scattering and ferromagnetic resonance techniques, we provide unambiguous experimental evidence for long-wavelength helimagnetic order at room temperature and magnetic properties similar to the bulk material. We obtain αintr = 0.0036 ± 0.0003 at 310 K for the intrinsic damping parameter. We probe the dynamics of the system by means of muon-spin rotation, indicating that the ground state is reached via a freezing out of slow dynamics. Our work paves the way towards the fabrication of thin films of chiral magnets that host certain spin whirls, so-called skyrmions, at room temperature and potentially offer integrability into modern electronics.
    [Show full text]
  • Magnetic Susceptibility and Chemical Shift
    A Magnetic susceptibility and chemical shift Susceptibility and chemical shift both deal with the interaction of electrons with a mag- netic field. Therefore, it is often difficult to distinguish these phenomena in MR images. The major difference between these two Zeemanlike influences is in the locality of their action and in their orientational dependence in an external polarizing field [1]. Chemical shift is a local phenomenon, acting on a single nucleus, while magnetic susceptibility acts on a larger scale. In this chapter, both phenomena are described and some consequences for MR imaging are illustrated by an infinite coaxial cylinder. Magnetic susceptibility The magnetic moments associated with atoms in materials are mainly determined by fac- tors originating from electrons and include the electron spin, electron orbital motion and the change in electron orbital motion caused by an imposed magnetic field. The existence and interaction of one or more of these phenomena in a material, determine the magnetic behavior. Also nuclear magnetism contributes to the magnetic moment, but it is weak and has a negligible effect on the bulk susceptibility [2]. Therefore, it will not be described in this appendix. Traditionally, classification of materials in groups according to their mag- netic behavior resulted in a division into groups according to the bulk susceptibility. The first group includes materials with negative and small susceptibility (χ = O( 10−5)) and includes e.g. copper, silver, bismuth and gold. These materials are called diamagnetic.− Paramagnetic materials have a small, positive susceptibility (χ = O(10−3) O(10−5)) and include aluminum, manganese, platinum and titanium.
    [Show full text]
  • Xi Magnetic Fields and Matter
    XI MAGNETIC FIELDS AND MATTER 11.1 Magnetic media and (magnetic) dipoles The magnetic properties of matter are due to the motion of the electric charges that constitute matter (mainly electrons). This idea originated with Ampère. Spin magnetic moments are also important, but for the purposes of the present discussion they also can be understood as circulating electric currents. A general distribution of currents will produce a very complicated magnetic field. As in the electric case, however, most of the magnetic properties of matter can be explained in terms of dipoles. Here case they are magnetic dipoles. Consider a small loop of area da with a current I flowing around it. The dm magnetic dipole moment dm is defined by I dm = Ida. (11.1) One can calculate the magnetic field away from the loop. When the distance is large compared with the dimension of the loop this gives the dipole approximation to the field. The result is similar to that for the electric field of an electric dipole. At large distances the field varies as B ~ 1/r2, as in the electric case. The bulk magnetic behaviour of matter is described in terms of the magnetisation vector M. This is defined as the total M dipole moment per unit volume. m M = Nm (11.2) where N is the number of dipoles of moment m, per unit volume. 11.2 Diamagnetism and paramagnetism The electric properties of matter were quantified in terms of the change in the capacitance of a capacitor when the material was placed between the plates.
    [Show full text]
  • Helimagnetism in Mnbi2se4 Driven by Spin-Frustrating Interactions Between Antiferromagnetic Chains
    crystals Article Helimagnetism in MnBi2Se4 Driven by Spin-Frustrating Interactions Between Antiferromagnetic Chains Judith K. Clark 1,†, Chongin Pak 1,2,†, Huibo Cao 3 and Michael Shatruk 1,2,* 1 Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306, USA; jkr17e@my.fsu.edu (J.K.C.); cpak@asc.magnet.fsu.edu (C.P.) 2 National High Field Magnetic Laboratory, Tallahassee, FL 32310, USA 3 Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA; caoh@ornl.gov * Correspondence: shatruk@chem.fsu.edu † Both authors contributed equally to this work. Abstract: We report the magnetic properties and magnetic structure determination for a linear- chain antiferromagnet, MnBi2Se4. The crystal structure of this material contains chains of edge- sharing MnSe6 octahedra separated by Bi atoms. The magnetic behavior is dominated by intrachain antiferromagnetic (AFM) interactions, as demonstrated by the negative Weiss constant of −74 K obtained by the Curie–Weiss fit of the paramagnetic susceptibility measured along the easy-axis magnetization direction. The relative shift of adjacent chains by one-half of the chain period causes spin frustration due to interchain AFM coupling, which leads to AFM ordering at TN = 15 K. Neutron diffraction studies reveal that the AFM ordered state exhibits an incommensurate helimagnetic structure with the propagation vector k = (0, 0.356, 0). The Mn moments are arranged perpendicular to the chain propagation direction (the crystallographic b axis), and the turn angle around the helix ◦ Citation: Clark, J.K.; Pak, C.; Cao, H.; is 128 . The magnetic properties of MnBi2Se4 are discussed in comparison to other linear-chain Shatruk, M.
    [Show full text]
  • Artificial Helical Nanomagnets
    Artificial helical nanomagnets A.A.Fraerman1, B.A.Gribkov1, S.A.Gusev1, B. Hjorvarsson2, A.Yu.Klimov1, V.L.Mironov1, D.S.Nikitushkin1, V.V.Rogov1, S.N.Vdovichev1, H.Zabel3 1Institute for Physics of Microstructures RAS, Nizhny Novgorod, Russia 2Uppsala University, Uppsala, Sweden 3Ruhr-Universitet, Bochum, Germany Electronic mail: andr@ipm.sci-nnov.ru We demonstrate the existence of a helical state in patterned multilayer nanomagnets. The artificial helimagnets consist of a stack of single domain ferromagnetic disks separated by insulating nonmagnetic spacers. The spiral state is shown to originate from the magnetostatic interaction between nearest and next nearest neighbouring single-domain disks in the stack. Since the magnetostatic interaction for such disks is rather strong, the helical state should be stable at room temperature. The helimagnets were fabricated from a [Co/Si]×3 multilayer using electron beam lithography. The helical state was confirmed by a magnetic stray field analysis using magnetic force microscopy. PACS numbers: 68.37.Rt, 75.75.+a, 75.70.Cn Helical magnets are of continued interest because of their unusual thermodynamic, optical, and magneto transport properties [1-9]. Helical magnetic ordering has previously been observed in natural crystals. For instance, a helical magnetization distribution with a spiral vector perpendicular to the close– packed planes is formed in holmium single crystals at temperatures below 133 K [1]. As a rule, helicoidal ordering in crystals appears to result from long-range interactions between the localized magnetic moments of atoms. In this Letter, we will show that a helical magnetization distribution can also be realized in artificial magnetic nanostructures.
    [Show full text]
  • Complex Magnetism in Noncentrosymmetric Magnets
    University of Tennessee, Knoxville TRACE: Tennessee Research and Creative Exchange Doctoral Dissertations Graduate School 8-2013 Complex magnetism in noncentrosymmetric magnets Nirmal Jeevi Ghimire nghimire@utk.edu Follow this and additional works at: https://trace.tennessee.edu/utk_graddiss Part of the Condensed Matter Physics Commons Recommended Citation Ghimire, Nirmal Jeevi, "Complex magnetism in noncentrosymmetric magnets. " PhD diss., University of Tennessee, 2013. https://trace.tennessee.edu/utk_graddiss/2427 This Dissertation is brought to you for free and open access by the Graduate School at TRACE: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Doctoral Dissertations by an authorized administrator of TRACE: Tennessee Research and Creative Exchange. For more information, please contact trace@utk.edu. To the Graduate Council: I am submitting herewith a dissertation written by Nirmal Jeevi Ghimire entitled "Complex magnetism in noncentrosymmetric magnets." I have examined the final electronic copy of this dissertation for form and content and recommend that it be accepted in partial fulfillment of the requirements for the degree of Doctor of Philosophy, with a major in Physics. David Mandrus, Major Professor We have read this dissertation and recommend its acceptance: Takeshi Egami, Elbio Dagotto, Stephen E. Nagler Accepted for the Council: Carolyn R. Hodges Vice Provost and Dean of the Graduate School (Original signatures are on file with official studentecor r ds.) Complex magnetism in noncentrosymmetric magnets A Dissertation Presented for the Doctor of Philosophy Degree The University of Tennessee, Knoxville Nirmal Jeevi Ghimire August 2013 c by Nirmal Jeevi Ghimire, 2013 All Rights Reserved. ii Dedicated to my parents. iii Acknowledgements I would like to express my thank and appreciation to my thesis advisor Dr.
    [Show full text]
  • Engineering Helimagnetism in Mnsi Thin Films S
    Engineering helimagnetism in MnSi thin films S. L. Zhang, R. Chalasani, A. A. Baker, N.-J. Steinke, A. I. Figueroa, A. Kohn, G. van der Laan, and T. , Hesjedal Citation: AIP Advances 6, 015217 (2016); doi: 10.1063/1.4941316 View online: http://dx.doi.org/10.1063/1.4941316 View Table of Contents: http://aip.scitation.org/toc/adv/6/1 Published by the American Institute of Physics AIP ADVANCES 6, 015217 (2016) Engineering helimagnetism in MnSi thin films S. L. Zhang,1 R. Chalasani,2 A. A. Baker,1,3 N.-J. Steinke,4 A. I. Figueroa,3 A. Kohn,2 G. van der Laan,3 and T. Hesjedal1,a 1Department of Physics, Clarendon Laboratory, University of Oxford, Oxford, OX1 3PU, United Kingdom 2Department of Materials Science and Engineering, Tel Aviv University, Ramat Aviv 6997801, Tel Aviv, Israel 3Magnetic Spectroscopy Group, Diamond Light Source, Didcot, OX11 0DE, United Kingdom 4ISIS, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0QX, United Kingdom (Received 22 November 2015; accepted 15 January 2016; published online 29 January 2016) Magnetic skyrmion materials have the great advantage of a robust topological magnetic structure, which makes them stable against the superparamagnetic ef- fect and therefore a candidate for the next-generation of spintronic memory de- vices. Bulk MnSi, with an ordering temperature of 29.5 K, is a typical skyrmion system with a propagation vector periodicity of ∼18 nm. One crucial prerequi- site for any kind of application, however, is the observation and precise control of skyrmions in thin films at room-temperature. Strain in epitaxial MnSi thin films is known to raise the transition temperature to 43 K.
    [Show full text]
  • Topological Metastability Supported by Thermal Fluctuation Upon Formation
    www.nature.com/scientificreports OPEN Topological metastability supported by thermal fuctuation upon formation of chiral soliton lattice in CrNb3S6 T. Honda1, Y. Yamasaki1,2,3,4*, H. Nakao1, Y. Murakami1, T. Ogura5, Y. Kousaka6 & J. Akimitsu7 Topological magnetic structure possesses topological stability characteristics that make it robust against disturbances which are a big advantage for data processing or storage devices of spintronics; nonetheless, such characteristics have been rarely clarifed. This paper focused on the formation of chiral soliton lattice (CSL), a one-dimensional topological magnetic structure, and provides a discussion of its topological stability and infuence of thermal fuctuation. Herein, CSL responses against change of temperature and applied magnetic feld were investigated via small-angle resonant soft X-ray scattering in chromium niobium sulfde ( CrNb3S6 ). CSL transformation relative to the applied magnetic feld demonstrated a clear agreement with the theoretical prediction of the sine- Gordon model. Further, there were apparent diferences in the process of chiral soliton creation and annihilation, discussed from the viewpoint of competing between thermal fuctuation and the topological metastability. Magnets with chiral crystal structure provide a good platform for exploring non-trivial spin textures due to Dzyaloshinskii-Moriya (DM) interaction which comes from the spin-orbit interaction and the lack of inver- sion symmetry of crystals. In these years, spin textures with topological features in the chiral magnets have been intensively investigated because of their promising potential for developing novel spintronics devices. For example, skyrmions, topological magnetic structures, show a triangle crystallization of the stable magnetic whirls that emerge in the 2D or 3D magnetic system1.
    [Show full text]
  • Strain-Modulated Helimagnetism and Emergent Magnetic Phase Diagrams
    Strain-modulated helimagnetism and emergent magnetic phase diagrams in highly crystalline MnP nanorod films Richa Pokharel Madhogaria1, Chang-Ming Hung1, Baleeswaraiah Muchharla1, Anh Tuan Duong2,*, Raja Das2, Pham Thanh Huy2, Sunglae Cho3, Sarath Witanachchi1, Hariharan Srikanth1,*, and Manh-Huong Phan1,* 1 Department of Physics, University of South Florida, Tampa, Florida 33620, USA 2 Phenikaa Research and Technology Institute, Phenikaa University, Yen Nghia, Ha-Dong District, Hanoi, 10000, Viet Nam 3 Department of Physics and Energy Harvest-Storage Research Center, University of Ulsan, Ulsan 680-749, Republic of Korea ABSTRACT We explore strain-modulated helimagnetism in highly crystalline MnP nanorod films grown on Si(100) substrates using molecular beam epitaxy. The strained MnP film exhibits a paramagnetic to ferromagnetic (PM-FM) phase transition at TC ~ 279 K, and the FM to helical phase transition at TN ~ 110 K. The value of TN is greater than TN ~ 47 K for the MnP single crystal, indicating strong strain-modulated helimagnetic states in the MnP nanorod film. The presence of significant thermal hysteresis in the helical phase indicates coexistence of competing magnetic interactions, leading to the first-order metamagnetic transition. Similar to its single crystal counterpart, an anisotropic magnetic effect is observed in the MnP film, which is independently confirmed by magnetic hysteresis loop and radio-frequency transverse susceptibility (TS) measurements. The evolution of screw (SCR) to CONE and FAN phase is precisely tracked from magnetization versus 1 magnetic field/temperature measurements. The temperature dependence of the anisotropy fields, extracted from the TS spectra, yields further insight into the competing nature of the magnetic phases.
    [Show full text]
  • Hard Condensed Matter
    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.
    [Show full text]
  • Magnetism Low Frequency Metal / High Frequency Insulator
    Magnetism low frequency metal / high frequency insulator Ibach & Lueth ITO Aluminum Conducting transparent contacts for LEDs and Solar cells ne2 2 p m Windows that reflect infrared 0 Reflection of radio waves from ionosphere Intraband transitions When the bands are parallel, there is a peak in the absorption (") Ekcv() Ek () Intraband (d-band) absorption Ibach &Lueth 1 Ry = 13.6 ev Institute of Solid State Physics Technische Universität Graz Magnetism diamagnetism paramagnetism ferromagnetism (Fe, Ni, Co) ferrimagnetism (Magneteisenstein) antiferromagnetism helimagnetism superparamagnetism spin glass 2222 2 22ZeAABe ZZe H iA iAiAijAB22mmeA, 444000 r iAijAB r r Coulomb interactions cause ferromagnetism not magnetic interactions. Institute of Solid State Physics Technische Universität Graz Magnetism magnetic intensity B 0 HM magnetic induction field magnetization M H is the magnetic susceptibility < 0 diamagnetic > 0 paramagnetic -5 is typically small (10 ) so B 0H Diamagnetism A free electron in a magnetic field will travel in a circle Bapplied Binduced The magnetic created by the current loop is opposite the applied field. Diamagnetism Dissipationless currents are induced in a diamagnet that generate a field that opposes an applied magnetic field. Current flow without dissipation is a quantum effect. There are no lower lying states to scatter into. This creates a current that generates a field that opposes the applied field. = -1 superconductor (perfect diamagnet) ~ -10-6 -10-5 normal materials Diamagnetism is always present but is often overshadowed by some other magnetic effect. Levitating diamagnets NOT: Lenz's law Levitating pyrolytic carbon d V dt Levitating frogs for water is -9.05 10-6 16 Tesla magnet at the Nijmegen High Field Magnet Laboratory http://www.hfml.ru.nl/froglev.html Andre Geim 2000 Ig Nobel Prize for levitating a frog with a magnet Diamagnetism A dissipationless current is induced by a magnetic field that opposes the applied field.
    [Show full text]