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Ferromagnetic Quantum Critical Point Avoided by the Appearance Of Ames Laboratory Publications Ames Laboratory 7-15-2016 Ferromagnetic Quantum Critical Point Avoided by the Appearance of Another Magnetic Phase in LaCrGe3 under Pressure Valentin Taufour Ames Laboratory, [email protected] Udhara S. Kaluarachchi Iowa State University, [email protected] Rustem Khasanov Paul Scherrer Institute Manh Cuong Nguyen Ames Laboratory, [email protected] Zurab Guguchia Paul Scherrer Institute Follow this and additional works at: http://lib.dr.iastate.edu/ameslab_pubs See next page for additional authors Part of the Condensed Matter Physics Commons, and the Engineering Physics Commons The ompc lete bibliographic information for this item can be found at http://lib.dr.iastate.edu/ ameslab_pubs/394. For information on how to cite this item, please visit http://lib.dr.iastate.edu/ howtocite.html. This Article is brought to you for free and open access by the Ames Laboratory at Iowa State University Digital Repository. It has been accepted for inclusion in Ames Laboratory Publications by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Authors Valentin Taufour, Udhara S. Kaluarachchi, Rustem Khasanov, Manh Cuong Nguyen, Zurab Guguchia, Pabitra Kumar Biswas, Pietro Bonfà, Roberto De Renzi, Xiao Lin, Stella K. Kim, Eun Deok Mun, Hyunsoo Kim, Yuji Furukawa, Cai-Zhuang Wang, Kai-Ming Ho, Sergey L. Bud'ko, and Paul C. Canfield This article is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/ameslab_pubs/394 week ending PRL 117, 037207 (2016) PHYSICAL REVIEW LETTERS 15 JULY 2016 Ferromagnetic Quantum Critical Point Avoided by the Appearance of Another Magnetic Phase in LaCrGe3 under Pressure Valentin Taufour,1,* Udhara S. Kaluarachchi,1,2 Rustem Khasanov,3 Manh Cuong Nguyen,1 Zurab Guguchia,3 Pabitra Kumar Biswas,4 Pietro Bonfà,5 Roberto De Renzi,5 Xiao Lin,2 Stella K. Kim,1,2 Eun Deok Mun,2 Hyunsoo Kim,2 Yuji Furukawa,1,2 Cai-Zhuang Wang,1 Kai-Ming Ho,1,2 Sergey L. Bud’ko,1,2 and Paul C. Canfield1,2 1The Ames Laboratory, U.S. Department of Energy, Iowa State University, Ames, Iowa 50011, USA 2Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA 3Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland 4ISIS Pulsed Neutron and Muon Source, STFC Rutherford Appleton Laboratory, Harwell Campus, Didcot, Oxfordshire OX11 0QX, United Kingdom 5Dipartimento di Fisica e Scienze della Terra, Parco Area delle Scienze 7/A, I-43124 Parma, Italy (Received 23 March 2016; published 13 July 2016) The temperature-pressure phase diagram of the ferromagnet LaCrGe3 is determined for the first time from a combination of magnetization, muon-spin-rotation, and electrical resistivity measurements. The ferromagnetic phase is suppressed near 2.1 GPa, but quantum criticality is avoided by the appearance of a magnetic phase, likely modulated, AFMQ. Our density functional theory total energy calculations suggest a near degeneracy of antiferromagnetic states with small magnetic wave vectors Q allowing for the potential of an ordering wave vector evolving from Q ¼ 0 to finite Q, as expected from the most recent theories on ferromagnetic quantum criticality. Our findings show that LaCrGe3 is a very simple example to study this scenario of avoided ferromagnetic quantum criticality and will inspire further study on this material and other itinerant ferromagnets. DOI: 10.1103/PhysRevLett.117.037207 Systems with a quantum phase transition (QPT), a phase parameters to tune a system towards a QPT but usually limits transition that occurs at 0 K, have revealed a wide variety of the number of experimental techniques that can be used to enigmatic phenomena. The case of the paramagnetic to probe an eventual new phase. In this study, resistivity ferromagnetic (PM-FM) QPT itself can lead to various measurements are used for a precise mapping of the temper- phase diagrams with the occurrence of tricritical wings ature-pressure phase diagram of LaCrGe3.Wecombinethese [1–3], a quantum Griffiths region [4,5], superconductivity with magnetization and muon-spin-rotation (μSR) measure- [2,6–9], or non-Fermi liquid behavior [10]. Several theories ments that probe the new phase AFMQ and show that AFMQ have been proposed to explain these intriguing effects has a similar magnetic moment as the FM phase but without [11–14]. Current theoretical proposals suggest that a net macroscopic magnetization. Finally, using thermody- continuous PM-FM QPT is not possible in clean, fully namic considerations as well as total energy calculations, we ordered systems. Instead, the transition can be of the first show that there is a near degeneracy of AFM ordered states order, or a modulated magnetic phase can appear [15–21].In near 2 GPa that can allow for the evolution of an ordering this Letter, we identify a new system, the compound wave vector from Q ¼ 0 to Q>0. Taken together, these data LaCrGe3, where a continuous PM-FM QPT under pressure firmly establish LaCrGe3 as a clear example of avoided is avoided by the appearance of a magnetic phase, most ferromagnetic quantum criticality by the appearance of likely a modulated phase characterized by a small wave modulated magnetic phase. vector Q. LaCrGe3 provides a clean example of a simple 3d- LaCrGe3 crystallizes in the hexagonal BaNiO3-type shell transition metal system in which such a phase appears. structure [space group P63=mmc (194)] [22,23]. At ambi- Long-wavelength correlation effects are essential to the ent pressure, LaCrGe3 is ferromagnetic below the Curie appearance of the modulated magnetic phase (AFMQ), which temperature TC ¼ 85 K [24] with an ordered magnetic is, therefore, characterized by a small wave vector Q [15].In moment at low temperature of 1.25 μB=Cr aligned along order to study such phases experimentally, it is necessary to the c axis [23,24]. This rather small value of the magnetic identify a system with a FM state that can be tuned to a QPT moment compared with the effective moment above TC μ ¼ 2 4 μ = using a clean tuning parameter. When chemical substitutions ( eff . B Cr) suggests some degree of delocalization are used to drive the PM-FM transition to 0 K, defects (and of the magnetism [24,25] in agreement with band-structure sometimes even changes in band filling) are inevitably calculations [22]. introduced. Such quenched disorder is expected to smear Figure 1(a) shows the temperature-pressure phase dia- the QPTs [13]. Pressure is considered as one of the cleanest gram of LaCrGe3 obtained from resistivity, magnetization, 0031-9007=16=117(3)=037207(6) 037207-1 © 2016 American Physical Society week ending PRL 117, 037207 (2016) PHYSICAL REVIEW LETTERS 15 JULY 2016 -6 (a) 100 250x10 ρ LaCrGe3 0.1 T H || c LaCrGe3 d /dT max Lifshitz dρ/dT 0 GPa 80 min 0.5 point ρ 200 d /dT mid 0.9 λ 1.48 60 µSR PC 1.84 µSR Bint 150 (K) 1.95 T M 40 2.2 FM (a.u.) M 100 AFMQ 20 ? 50 0 (b) 100 2 K 0 80 cm) 0 40 80 120 60 T (K) μΩ ( 40 ρ 20 FM AFMQ PM? FIG. 2. Temperature dependence of the magnetization at 0 0 1 2 3 4 5 6 7 various pressures. The Curie temperature is indicated by arrows at the position of the change of slope, as illustrated by lines for p (GPa) the curve at 0 GPa. Data are offset for clarity. Because such measurement is sensitive to the large background of the pressure FIG. 1. (a) Temperature-pressure phase diagram of LaCrGe3 cell with comparison to the sample signal, the applied field is from various measurements showing the FM and AFMQ. rather low (0.1 T). Since at such low field the magnetization does (b) Pressure dependence of the resistivity at 2 K. Different not reach saturation, the change of magnetization at low temper- symbols (cross, open circle, filled circle) represent data of ature is better determined by μSR experiments. different samples from different pressure runs. [Fig. 3(d)]. For p<1.4 GPa, a simultaneous increase of B λ T and μSR measurements, which will be described below. int and PC can be observed upon cooling through C, The ferromagnetic phase is suppressed at p ¼ 2.1 GPa, indicating that the sample is ferromagnetic and induces a and a modulated magnetic phase labeled AFMQ is observed field in the pressure cell body. At 1.78(1) GPa, the increase for 1.5 <p<5.3 GPa. The very steep pressure depend- (a) (b) ence of TC near 2.1 GPa and the abrupt doubling of the 0.5 GPa 250 LaCrGe3 0.15 residual (T ¼ 2 K) resistivity shown in Fig. 1(b) suggest 0.20 0.5 200 1.3 that the FM-AFMQ transition is of the first order. Indeed, 1.3 GPa 1.78 dT =dp 2.18 the Clausius-Clapeyron relation imposes that C 0.20 T ¼ 0 150 tends to infinity for a first-order transition at K, (mT) 1.78 GPa int and a peak in the resistivity rather than a discontinuous step B 100 is expected for a second-order quantum phase transition asymmetry 0.20 [26–28]. The discontinuous step disappears near 40 K [29], 2.18 GPa 50 0.20 above which the resistivity isotherms are a continuous 0 function of pressure. Therefore, there exists a tricritical 0 0.1 0.2 0.3 0.4 0.5 0 40 80 120 t (µs) T (K) point near 40 K below which the FM-AFMQ transition is (c) (d) 0.2 of the first order. The merging of the three transition lines 1.29 GPa 1.4 0.46 0 1.2 1.29 (FM-AFMQ, FM-PM, and AFMQ-PM) is called the -0.2 1.79 0.2 ) 1.0 2.3 Lifshitz point [52].
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