Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session B07: Correlated Magnetism and Other Ordered Phases |
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Sponsoring Units: DCMP GMAG Chair: Kaya Wei, Florida State University Room: BCEC 109B |
Monday, March 4, 2019 11:15AM - 11:27AM |
B07.00001: Enhanced Magnetic Ordering in Sm Metal under Extreme Pressure Yuhang Deng, James S Schilling The dependence of the magnetic ordering temperature To of Sm metal was determined through four-point electrical resistivity measurements to pressures as high as 127 GPa. A strong increase in To with pressure was observed above 40 GPa. In this pressure range Sm ions alloyed in dilute concentration with superconducting Y exhibit giant Kondo pair breaking. Both results suggest that for pressures above 40 GPa Sm enters a highly correlated electron state, likely related to a Kondo lattice, with an unusually high value of To. Similar results were found previously for Nd [1], Tb [2], and Dy [3] and their dilute magnetic alloys with superconducting Y. Both Y(Sm) and Y(Nd) alloys display record-high pair breaking ΔTc as large as 40 K/at.%. |
Monday, March 4, 2019 11:27AM - 11:39AM |
B07.00002: Superparamagnetic clusters in antiferromagnetic Eu0.52Ca0.48B6 seen by Small Angle Neutron Scattering (SANS) Gabrielle Beaudin, Andrea Bianchi, Mark Laver, Robert Arnold Since the term was introduced by Pekar in 1946, polarons have been thought to underpin a range of prominent phenomena from high-Tc superconductivity to colossal magnetoresistance. Polarons are quasiparticles consisting of charge carriers ``dressed'' by lattice distortions. Similarly, magnetic polarons are charge carriers dressed with spins. In the europium chalcogenides, magnetic polarons are thought to be formed as a spin polarization of the mobile charge carriers by the localized 4f moments. This leads to the formation of magnetic ``bubbles'' and the localization of charge carriers within them. Here we report on experiment which extends an earlier experiment on EuB6 where SANS indicated the presence of magnetic polarons. The experiment was carried out at the Institut Laue Langevin (ILL) in Grenoble. It shows the presence of superparamagnetic clusters well above the critical temperature in 48% Ca doped-EuB6. Unlike EuB6, Eu0.52Ca0.48B6 does not undergo an insulator to metal phase transition, and its resistivity grows rapidly below 10 K. A metallic state can be obtained through the application of a magnetic field greater than 2 T. In Eu0.52Ca0.48B6, the charge carrier stay trapped inside the magnetic polarons, leading to an increasing resistivity at lower temperature. |
Monday, March 4, 2019 11:39AM - 11:51AM |
B07.00003: NMR Studies of TmVO4 Zhipan Wang, Ziwen Mei, Paulo Menegasso, Tanat Kissikov, Pierre Massat, Ian R Fisher, Nicholas Curro TmVO4 undergoes a tetragonal to orthorhombic structural phase transition below 2.2K due to a cooperative Jahn-Teller distortion. The Tm ions experience a crystal-field effect with a non-Kramer’s ground state doublet. We have performed 51V NMR in a single crystal to investigate the role of magnetic and quadrupolar fluctuations. We find that the spin lattice relaxation rate varies strongly with field orientation, which reflects the role of quadrupolar(nematic) fluctuations near the critical temperature. We have also observed strong angular dependence of the 51V NMR Knight shift. |
Monday, March 4, 2019 11:51AM - 12:03PM |
B07.00004: NMR Studies of Nematicity in TmVO4 and TmAsO4 Ziwen Mei, Zhipan Wang, Paulo Menegasso, Pierre Massat, Ian R Fisher, Nicholas Curro The crystal field ground state of Tm ions in certain crystal symmetries is a non-Kramers doublet, with a vanishing g-factor. In such cases strain can couple to the quadrupolar moment of the Tm ions, and a cooperative Jahn-Teller effect leads to Ising orbital-nematic order of the Tm moments. Application of a magnetic field along the c-axis suppresses the nematic order continuously and gives rise to a nematic quantum critical point. We have studied the critical nematic fluctuations via 51V and 75As NMR in TmVO4 and TmAsO4. These nuclei have quadrupolar moments that couple to the nematic degrees of freedom of the Tm. Fluctuations of both the Tm magnetic moments and the quadrupolar moments contribute to the spin-lattice relaxation of the nuclei, and we demonstrate how both the dynamical magnetic and dynamical nematic susceptibilities can be extracted from the spin-lattice relaxation rate. |
Monday, March 4, 2019 12:03PM - 12:15PM |
B07.00005: Electronic correlations in potential new rare-earth permanent magnet materials Anna Galler, Leonid Pourovskii, Silke Biermann Designing new materials for permanent magnet applications is currently a very active field of research. While, at present, the best permanent magnets are based on the expensive rare-earth elements Nd, Sm or Dy (e.g. Nd2Fe14B), efforts are made to replace them with more available elements like Ce, with the hope to discover compounds with even better performance and lower production costs. Theoretical efforts to assist this quest encounter challenges related to the correlated nature of the rare-earth 4f states. In particular, in the family of potential Ce-based permanent magnet materials a key question is the localized vs. heavy-fermion behavior of the Ce-4f electrons. In this context, we investigate the role of electronic correlations in CeFe2, CeFe12 and CeFe11Ti from first principles by using combined density functional and dynamical mean-field theory. We solve the corresponding quantum impurity problem by means of a continuous-time Quantum Monte Carlo solver and analyze the resulting electronic structure focusing on the degree of localization of the Ce-4f states as well as the magnetic properties of the compounds. |
Monday, March 4, 2019 12:15PM - 12:27PM |
B07.00006: Microscopic Theory of Γ3 Quadrupole Ordering in Pr Compounds on the Basis of a j-j Coupling Scheme Ryosuke Yamamura, Takashi Hotta In recent decades, multipole ordering in f2-electron systems such as Pr and U compounds have attracted continuous attention in the research field of condensed matter physics. In fact, peculiar modulated antiferro non-Kramers Γ3 quadrupole ordering in PrPb3 has been reported in 2005 [1], but the mechanism has been still under debate. |
Monday, March 4, 2019 12:27PM - 12:39PM |
B07.00007: Investigating 4f ferrroquadrupolar phase transitions: local moment realizations of nematicity Elliott Rosenberg, Ian R Fisher Electronic nematicity, in which the electronic degrees of freedom break the rotational symmetry of the lattice, has been exhibited by many materials including various high-temperature superconductors. A local realization of electronic nematicity is also seen in 4f intermetallic materials undergoing ferroquadrupolar order. In these materials the lattice of local 4f electronic multiplets collectively and spontaneously break the rotational symmetry of the point group of the lattice. Here we measure the quadrupole-strain (nematic) susceptibility of TmAg2, which exhibits a ferroquadrupolar phase transition at 5.0K. We implement an elastoresistivity technique previously used in probing another 4f intermetallic, YbRu2Ge2 , and extend this technique to investigate the nematic behavior of TmAg2 while applying a “transverse” magnetic field to suppress the ferroquadrupolar phase transition to 0K. |
Monday, March 4, 2019 12:39PM - 12:51PM |
B07.00008: Ferromagnetic spin correlations in the filled skutterudite SrFe4As12 revealed by 75As NQR-NMR studies Yuji Furukawa, Qing-Ping Ding, Khusboo Rana, Kohei Nishine, Jun-ichi Hayashi, Yukihiro Kawamura, Chihiro Sekine Recently new filled-skutterudite compounds SrT4As12 (T = Fe, Ru, Os) have been synthesized, which provides a new opportunity of systematic studies of the effects of different d electron of 3d, 4d and 5d in the systems. In this study, as the first step for the systematic studies, we have carried out nuclear quadrupole resonance (NQR) and nuclear magnetic resonance (NMR) measurements on the filled skutterudite SrFe4As12 in order to investigate the magnetic properties from a microscopic point of view. Using the NQR spectra under small magnetic field, we have succeeded in determining Knight shift K. The temperature dependences of both K and the nuclear spin-lattice relaxation rate divided by temperature, 1/T1T, have been reasonably explained by the simple model in which a concave-shaped band structure near the Fermi energy is assumed. The Korringa ratio parameter is found to be much smaller than unity, indicating the existence of ferromagnetic fluctuations. These NMR/NQR results evidence that SrFe4As12 is a metal with ferromagnetic spin correlations. |
Monday, March 4, 2019 12:51PM - 1:03PM |
B07.00009: Antiferromagnetic order in Sr(Co1-xNix)2As2 revealed by single-crystal neutron diffraction John Wilde, Andreas Kreyssig, David Vaknin, Sangeetha N. S., Bing Li, Benjamin Ueland, David C Johnston, Robert McQueeney, Alan Ira Goldman SrCo2As2 has the same tetragonal lattice as the 122 Fe-based high Tc superconductors. It does not order magnetically, but inelastic neutron scattering experiments find antiferromagnetic (AF) fluctuations found in many of the 122 superconductors. Here we show results from neutron diffraction and magnetization experiments on single-crystals of Sr(Co1-xNix)2As2. However, the AF order is not stripe-type. Instead, the AF structure consists of ferromagnetic layers (with moments in the layer) that are stacked along c with an incommensurate propagation vector (0, 0, qz). The propagation vector is doping dependent, suggesting spin density wave order. Using high-energy x-ray diffraction, we also find no evidence for a structural phase transition accompanying the AF order. |
Monday, March 4, 2019 1:03PM - 1:15PM |
B07.00010: Electronic Structure and the Origin of the Phase Transition in BaAg2As2 Revealed by ARPES and REXS Studies Xia Lou Transition metal pnictides in 122 families are rich with fantastic quantum phenomena such as spin density wave (SDW) in BaFe2As2[1], superconductivity (SC) and charge density wave (CDW) in SrPt2As2[2] and BaPt2As2[3]. In the meanwhile, BaPt2As2 and SrPt2As2 shares CaBe2Ge2-type structure while BaFe2As2 crystallizes in ThCr2Si2-type structure. Studying the interplay among SDW, SC and CDW and their relationship with crystal structure and structural transition is of wide interests. BaAg2As2, as a newly-discovered transition metal pnictide adopted to ThCr2Si2-type structure, possess a phase transition at 138K in resistivity whose origin is still unknown[4]. To study the mechanism, we applied systematic angle-resolved photoemission spectroscopy (ARPES) combined with resonant elastic soft X-ray scattering (REXS) and identified the exact structural transition and density-wave-like transition in it for the first time. |
Monday, March 4, 2019 1:15PM - 1:27PM |
B07.00011: Neutron diffraction studies of the composition induced moment reorientation in antiferromagnetically ordered Ca1-xSrxCo2As2 Bing Li, Sangeetha N. S., John Wilde, Wei Tian, Andreas Kreyssig, Benjamin Ueland, David C Johnston, Alan Ira Goldman, Robert McQueeney ACo2As2 (A = Ca, Sr, Ba) are tetragonal itinerant magnets that display a dichotomy typical of their As-As hybridization-driven magnetoelastic interactions: CaCo2As2 has A-type antiferromagnetic (AFM) order with Co ordered moments aligned along c, and SrCo2As2 and BaCo2As2 do not order. Ca1-xSrxCo2As2 shows a series of magnetic phases, with transitions between them at x ≈ 0.2, 0.3, and 0.5. Magnetization data show A-type order as in CaCo2As2 for x < 0.2 and no magnetic order for x > 0.5. Here, we present and discuss quantitative results from neutron and high-energy x-ray diffraction experiments on single crystals with x = 0.25 and 0.40. Rather than A-type order, we find extremely weak magnetic Bragg peaks corresponding to a propagation vector of (0, 0, 0.5) for both samples. The ordered moment lies along c for x = 0.25 but in the ab plane for x = 0.40. No structural phase transitions accompany the AFM transitions. |
Monday, March 4, 2019 1:27PM - 1:39PM |
B07.00012: Electrical and Magnetic Properties of Layered CaMn2Bi2 Joanna Blawat, Xin Gui, Roshan Nepal, Ramakanta Chapai, Robert Cava, Weiwei Xie, Rongying Jin CaMn2Bi2 forms a hexagonal structure, consisting of alternately stacked Ca and Mn2Bi2 layers. Instead of ferromagnetic ordering seen in MnBi, CaMn2Bi2 orders antiferromagnetically below TN ~ 150 K, as reflected in the magnetization, specific heat, and electrical resistivity. Although it is considered as a narrow-gap semiconductor, our resistivity shows metallic behavior with a sharp drop at TN and a little bump at Tb ~ 20 K. Below Tb, large positive magnetoresistance with non-monotonic field dependence is observed in all current and magnetic field configurations. Its possible origin will be discussed. |
Monday, March 4, 2019 1:39PM - 1:51PM |
B07.00013: Electronic Structure and Magnetic Phase Transition in Double Perovskite La2-xNaxMnMoO6 (x=0, 0.5, 1.0, 1.5, 2.0) Dinesh Yadav, Bishnu Prasad Belbase, Shalika Ram Bhandari, Madhav Prasad Ghimire, Gopi Chandra Kaphle
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Monday, March 4, 2019 1:51PM - 2:03PM |
B07.00014: Neutron scattering study of the evolution from ferromagnetism to antiferromagnetism in NaCrSixGe2-xO6 pyroxenes Wei Tian, Jiaqiang Yan, Alexander I Kolesnikov, Brian Craig Sales NaCrGe2O6 and NaCrSi2O6 are isostructural compounds exhibiting different magnetic ground state. NaCrGe2O6 adopts a ferromagnetic ground state with Tc=6K, whereas NaCrSi2O6 orders antiferromagnetically at TN=3K. The complex magnetic behavior in Cr-based pyroxenes involves competition between direct and super-exchange magnetic interactions - a delicate balance that is sensitive to the Cr-Cr distance and chemical pressure. Here we present a systematic neutron scattering study of NaCrSixGe2-xO6 that reveals how the substitution of Ge by Si affects the evolution from ferromagnetism to antiferromagnetism in theses compounds. |
Monday, March 4, 2019 2:03PM - 2:15PM |
B07.00015: Band structure induced electronic correlations in nickel and iron: van-Hove singularities vs. Earth's core conditions Andreas Hausoel, Michael Karolak, Ersoy Sasioglu, Alexander I. Lichtenstein, Karsten Held, Andrey A. Katanin, Alessandro Toschi, Giorgio Sangiovanni Some Bravais lattices have a particular geometry and can slow down the motion of Bloch electrons: a 'pre-localisation' due to band structure properties. Another known source of electronic localisation in solids is the Coulomb repulsion in partially-filled d- or f-orbitals, which leads to the formation of local magnetic moments. The combination of these two effects has been viewed so far as mainly an academic issue. Here we show with ab-initio calculations of unprecedented accuracy and model studies, that their synergy represents instead the underlying physical mechanism in two of the most important ferromagnets: nickel and iron. Furthermore in nickel, the van-Hove singularity is essential for ferromagnetism to appear. Nickel's electron-electron scattering rate is linear in temperature, in violation of the conventional Landau theory of metals. This is true even at Earth's-core conditions, at which iron is instead a good Fermi-liquid. The importance of nickel in models of geomagnetism may therefore be reconsidered. |
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