Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session B48: Frustrated Magnetism: Spinels, Pyrochlores, and Frustrated 3D Magnets I |
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Sponsoring Units: GMAG DMP Chair: Martin Mourigal, Georgia Tech Room: 395 |
Monday, March 13, 2017 11:15AM - 11:27AM |
B48.00001: Frustrated magnetism and magnetic reversal in inverse spinel Co$_{2}$VO$_{4}$ Pinaki Das, Y. Yiu, N. Anderson, Y. Liu, D. Vaknin, C. M. Naveen Kumar Vanadium oxide spinels with formula $A$V$_{2}$O$_{4}$ ($A$ = Co, Fe, Mn, etc.) have attracted much interest due to their intriguing physical properties but little attention has been paid to inverse vanadium oxide spinels of the form, $A_{2}$VO$_{4}$ ($A$ = Co or Fe). Here we report magnetization, X-ray and neutron diffraction, and XMCD measurements on high quality polycrystalline Co$_{2}$VO$_{4}$ sample that has been known as a magnetization-reversal system. Magnetic susceptibility measurements show a magnetic transition at $T_N$ = 165~K, with features that dramatically change below 100 K as external field ($H$) is increased. Interestingly, for $H \le 0.25$~T and $T < 75$~K, magnetization reversal is observed in field-cooled measurements which is also confirmed by the XMCD measurements that reveal a spin-flop of the B-site Co and V $L$-edges. X-ray and neutron diffraction measurements confirm its $Fd\bar{3}m$ symmetry, which remains unchanged from 300 to 2~K and indicate a single magnetic transition at $T_N = 165$~K. Analysis of the detailed neutron powder diffraction measurements of the magnetic structure will also be shown. [Preview Abstract] |
Monday, March 13, 2017 11:27AM - 11:39AM |
B48.00002: Glassy spin density wave states and frustrated Kondo chains on the pyrochlore lattice Jing Luo, Gia-Wei Chern We investigate the spin density wave (SDW) states in frustrated pyrochlore lattice with degenerate orbitals. The directional nature of $t_{2g}$ orbitals leads to a highly anisotropic electron conduction. In the leading order approximation, the pyrochlore magnet can be viewed as a cross-linking network of Kondo or double-exchange chains. In contrast to models based on Mott insulators, this itinerant magnetism approach provides a natural explanation for several spin and orbital superstructures observed in pyrochlore lattice. Here we show that a novel commensurate multiple-$\mathbf q$ SDW order characterized by Bragg peaks at $\langle \frac{1}{3},\frac{1}{3}, 1\rangle$ wavevectors is stabilized at low temperatures when the $t_{2g}$ band is $1/3$ or $2/3$ filled. Interestingly, the SDW phase exhibits a large number of quasi-degenerate meta-stable states. Through extensive Monte Carlo simulations, we provide strong evidence for the glassy nature of this SDW state. Finally, our results successfully describes the recent experimental observations on spinel GeFe$_2$O$_4$. \footnote{T. Zhou {\em et al.} APS March Meeting 2016, Abstract K5.00009} [Preview Abstract] |
Monday, March 13, 2017 11:39AM - 11:51AM |
B48.00003: Magnetic Properties of $A$-site Antiferromagnetic Spinels CoRh$_2$O$_4$ and CuRh$_2$O$_4$ Luwei Ge, Joshua Flynn, Joseph Paddison, Matthew Stone, Stuart Calder, Arthur Ramirez, Mas Subramanian, Martin Mourigal We characterize the magnetic properties of the $A$-site spinels CoRh$_2$O$_4$ and CuRh$_2$O$_4$ by means of thermodynamic and neutron scattering measurments and perform group theory analysis, Rietveld refinement, mean-field theory, and spin wave theory calculations to analyze our results. Our investigation reveals that CoRh$_2$O$_4$ is a canonical $S=3/2$ diamond-lattice Heisenberg antiferromagnet with a nearest neighbor exchange $J=0.63$ meV and a N\'eel temperature of 25 K. In CuRh$_2$O$_4$, the distorted diamond lattice leads to the development of an incommensurate helical order at 24 K. Strong reduction of the ordered moment is observed for the $S=1/2$ spins and reproduced by $1/S$ corrections to spin-wave theory. [Preview Abstract] |
Monday, March 13, 2017 11:51AM - 12:03PM |
B48.00004: Anisotropic exchange in ytterbium spinels Jeffrey Rau, Michel Gingras Recently, the possibility that competing strongly anisotropic exchange interactions may stabilize a range of unusual phenomena has attracted much interest. Examples include spin-orbit Mott insulators which may realize variants of Kitaev’s honeycomb model and quantum rare-earth pyrochlores which host order-by-disorder physics, strong multi-phase competition, and could potentially harbour a quantum spin ice ground state. In this talk, we consider exchange interactions in ytterbium pyrochlore spinels. These compounds have the same edge-sharing octahedra found in the Kitaev materials, but with the atomic physics and frustrated lattice of the rare-earth pyrochlores. We argue that the exchange in these compounds can be understood within the simple “charging approximation”. We then validate this framework on the well-characterized “breathing” pyrochlore Ba$_3$Yb$_2$Zn$_5$O$_{11}$, finding good agreement with the experimentally determined parameters. Turning to the Yb-based spinels, we find that the landscape of exchange parameters contains only two clear limits: a Heisenberg antiferromagnet and a ferromagnetic Kitaev exchange interaction. We further discuss the effect of relaxing the assumption of a perfect 90 degree bond angle and comment on applications to known Yb-based spinels. [Preview Abstract] |
Monday, March 13, 2017 12:03PM - 12:15PM |
B48.00005: Absence of nematic ordering transition in a diamond lattice: Application to FeSc2S4 Chandan Setty, Zhidong Leong, Shuyi Zhang, Philip Phillips Recent neutron scattering observations by Plumb et al [1] reveal that the ground state of FeSc2S4 is magnetic with two distinct Fe environments, instead of a quantum spin liquid as had been previously thought. Starting with the relevant O(N)-symmetric vector model of FeSc2S4, we study how the discrete (Z2) and continuous rotational symmetries are successively broken, yielding nematic and ordered phases. At high temperatures, we find that the nematic order parameter falls as T\textasciicircum \textbraceleft -$\backslash $gamma\textbraceright ($\backslash $gamma\textgreater 0), and therefore, FeSc2S4 is highly susceptible to the breaking of Ising symmetries, and explains the two distinct Fe environments that is present even at high temperatures, as seen by Mossbauer and far infrared optical spectroscopy. [1] K. Plumb, J. Morey, J. Rodriguez-Rivera, H. Wu, A. Podlesnyak, T. McQueen, and C. Broholm, arXiv preprint arXiv:1603.08033 (2016) [Preview Abstract] |
Monday, March 13, 2017 12:15PM - 12:27PM |
B48.00006: S = 1 on a Diamond Lattice in NiRh2O4 Juan Chamorro, Tyrel McQueen An S = 1 system has the potential of rich physics, and has been the subject of intense theoretical work. Extensive work has been done on one-dimensional and two-dimensional S = 1 systems, yet three dimensional systems remain elusive. Experimental realizations of three-dimensional S = 1, however, are limited, and no system to date has been found to genuinely harbor this. Recent theoretical work suggests that S = 1 on a diamond lattice would enable a novel topological paramagnet state, generated by fluctuating Haldane chains within the structure, with topologically protected end states. Here we present data on NiRh2O4, a tetragonal spinel that has a structural phase transition from cubic to tetragonal at T = 380 K. High resolution XRD shows it to have a tetragonally distorted spinel structure, with Ni2+ (d8, S = 1) on the tetrahedral, diamond sublattice site. Magnetic susceptibility and specific heat measurements show that it does not order magnetically down to T = 0.1 K. Nearest neighbor interactions remain the same despite the cubic to tetragonal phase transition. Comparison to theoretical models indicate that this system might fulfill the requirements necessary to have both highly entangled and topological behaviors. [Preview Abstract] |
Monday, March 13, 2017 12:27PM - 12:39PM |
B48.00007: High-pressure synthesis and characterizations of the R2Pt2O7 pyrochlores. Yunqi Cai, Qi Cui, Jinguang Cheng, Zhiling Dun, Haidong Zhou, Jie Ma, C. dela Cruz, Jiaqiang Yan, Xiang Li, Jianshi Zhou |
Monday, March 13, 2017 12:39PM - 12:51PM |
B48.00008: Abstract Withdrawn We study all components of the thermal conductivity tensor of complex magnets at high temperatures, focusing on the roles of dimensionality, anisotropic exchange, and applied fields. We formulate things particularly for lattices of corner-sharing simplexes and discuss applications to recent experiments in frustrated magnets. |
Monday, March 13, 2017 12:51PM - 1:03PM |
B48.00009: Effect of site disorder on the ground state of a frustrated spin dimer quantum magnet Alexander Hristov, Maxwell Shapiro, Minseong Lee, Linsey Rodenbach, Eun Sang Choi, Ju-Hyun Park, Tim Munsie, Graeme Luke, Ian Fisher Ba$_{3}$Mn$_{2}$O$_{8}$ is a geometrically frustrated spin dimer quantum magnet. Pairs of Mn $^{5+}$ ($S=1$) ions are strongly coupled via antiferromagnetic exchange to yield a singlet ground state, with excited triplet and quintuplet states. Isovalent substitution of V$^{5+}$ ($S=0$) for Mn “breaks” dimers, resulting in unpaired $S = 1$ spins, the ground state of which is investigated here for compositions spanning the range $0 \leq x\leq 1$ of Ba$_{3}$(Mn$_{1-x}$V$_{x}$)$_{2}$O$_{8}$. From a theoretical perspective, for dimers occupying an unfrustrated bipartite lattice, such site disorder is anticipated to yield long range magnetism for unpaired Mn spins both in the dilute limit where $x$ is small, a phenomena known as order-by-disorder, and in the proximity of $x=1/2$ where the system is maximally disordered and close to a percolation threshold. In this frustrated system, however, our experiments find evidence of spin freezing for six compositions $0.05 \leq x \leq 0.85$. In this regime, we find entropy removed at an energy scale independent of the freezing temperature. We discuss the possibility of a spin-glass to random singlet transition for critical compositions in the two dilute limits $x\to 0$ and $x\to 1$. [Preview Abstract] |
Monday, March 13, 2017 1:03PM - 1:15PM |
B48.00010: Investigation of the anomalous Hall effect in non-collinear and non-coplanar magnets Nakheon Sung, F Ronning, J. D. Thompson, E. D. Bauer Magnetic frustration causes non-collinear and non-coplanar spin structures including complicated helical and conical magnetic states. Interestingly, these magnets had been found to have a drastic effect on the conductivity of a material and may also lead to exotic states of matter, such as skyrmions in FeGe [1], and superconductivity in CrAs [2]. Because conduction electrons are affected by a fictitious magnetic field of astronomical strength in the topological spin structure of these magnets, which gives rise to a large anomalous Hall effect (AHE). The AHE in zero applied magnetic field was realized experimentally in spin liquid system Pr2Ir2O7 [3] and the antiferromagnet Mn3Sn [4]. However, the relationship between crystal structure and the magnetic states, or how structure influences the strength of the coupling of the magnetic moments to the conduction electrons, is not well understood yet. Here, we report measurements of the AHE in various non-collinear and non-coplanar magnets. [1] Nature Materials 10, 106--109 (2011) X. Z. Yu et al. [2] Nature Communications 5, 5508 (2014) Wei Wu et al. [3] Nature 463, 210 (2010) Y. Machida et al. [4] Nature 527, 212 (2015) S. Nakatsuji et al. [Preview Abstract] |
Monday, March 13, 2017 1:15PM - 1:27PM |
B48.00011: Structural and magnetic properties of the 5$d^2$ double perovskites Sr$_2 B$ReO$_6$ ($B$ $=$ Y, In) A.A. Aczel, Z. Zhao, D.T. Adroja, S. Calder, P.J. Baker, J.-Q. Yan We have performed magnetic susceptibility, heat capacity, neutron powder diffraction, and muon spin relaxation experiments to investigate the magnetic ground states of the 5$d^2$ double perovskites Sr$_2$YReO$_6$ and Sr$_2$InReO$_6$. We find that Sr$_2$YReO$_6$ is a spin glass, while Sr$_2$InReO$_6$ hosts a non-magnetic singlet state. By making detailed comparisons with other 5$d^2$ double perovskites, we argue that a delicate interplay between spin-orbit coupling, non-cubic crystal fields, and exchange interactions plays a key role in the great variation of magnetic ground states observed for this family of materials. [Preview Abstract] |
Monday, March 13, 2017 1:27PM - 1:39PM |
B48.00012: The amplitude mode in three-dimensional dimerized antiferromagnets Yanqi Qin, Anders Sandvik, Bruce Normand, Ziyang Meng The amplitude (Higgs) mode is a ubiquitous collective excitation related to spontaneous breaking of a continuous symmetry. We combine quantum Monte Carlo (QMC) simulations with stochastic analytic continuation to investigate the dynamics of the amplitude mode in a three-dimensional dimerized quantum spin system. We characterize this mode by calculating the spin and dimer spectral functions near the quantum critical point, finding that both the energies and the intrinsic widths satisfy field-theoretical scaling predictions. While the line width of the spin response is close to that observed in neutron scattering experiments on TlCuCl$_3$, the dimer response is significantly broader. Our results demonstrate that highly non-trivial dynamical properties are accessible by modern QMC and analytic continuation methods. [Preview Abstract] |
Monday, March 13, 2017 1:39PM - 1:51PM |
B48.00013: Phase diagram and high degeneracy points for generic anisotropic exchange on the garnet lattice Alexei Andreanov, Paul McClarty Garnet magnets with chemical formula RE$_3$Ga$_5$O$_{12}$ where RE is a rare earth ion have properties that are determined by a combination of geometrical frustration and strong spin-orbit coupling. The former arises from the RE structure which consists of two interpenetrating hyperkagome lattices while the latter leads, in general, to an anisotropy in the magnetic exchange. We systematically explore and describe the full phase diagram for the case of all nearest-neighbor interactions compatible with lattice symmetries and consider the role of fluctuations and further neighbor couplings around high degeneracy points in the phase diagram. [Preview Abstract] |
Monday, March 13, 2017 1:51PM - 2:03PM |
B48.00014: Anisotropic phase diagram of the rare-earth hyperkagome system Gd3Ga5O12 (GGG) Jeffrey Quilliam, Alexandre Rousseau, Jean-Michel Parent An understanding of the low-temperature properties of the hyperkagome system Gd$_3$Ga$_5$O$_{12}$ or GGG is a long-standing problem in the field of frustrated magnetism. The origins of spin liquid and exotic spin-glass phases in this material remain mysterious and even its precise magnetic phase diagram is still not firmly established. We have investigated the field-induced phase diagram of this material using the ultrasound velocity and attenuation technique at temperatures as low as 40 mK. Two different field orientations are tested, and give rise to significant quantitative and qualitative differences. Notably, two distinct field-induced antiferromagnetic phases are observed for field parallel to 110, consistent with recent results$^\ast$, whereas only one ordered phase is observed for a 100 orientation. The field dependence of the sound velocity and attenuation is also found to be anisotropic within the low-field spin liquid phase. \\ \\ $^\ast$ P. P. Deen \emph{et al.}, Phys. Rev. B {\bf 91}, 014419 (2015). [Preview Abstract] |
Monday, March 13, 2017 2:03PM - 2:15PM |
B48.00015: Magnetic Excitations in Multiferroic GdMn$_2$O$_5$. Sergey Poghosyan, Sergey Artyukhin Orthorhombic $R$Mn$_2$O$_5$ compounds recently attracted attention due to a complex frustrated ground state and unconventional excitations. $YMn_2O_5$ with non-magnetic rare earth (RE) shows incommensurate spiral state with spins in the neighbouring chains aligned at 90-degrees to each other [1]. RE ions with unquenched angular momentum enable the control of polarization by magnetic field in the multiferroic materials, such as $TbMn_2O_5$ [2]. Strongly $GdMn_2O_5$, with magnetic rare earth in S=7/2, L=0 state, exhibits a spiral state below 40K, that concedes to a commensurate state below $\sim30K$. The latter hosts large magnetically-induced polarization of 3600 $\mu C/m^2$ induced via Heisenberg exchange striction mechanism. This polarization changes by 5000 $\mu C/m^2$ under the external magnetic field [3]. Here we corroborate THz magnetoabsorption data with the microscopic modelling. The magnetic excitations are calculated using model Hamiltonian with parameters extracted from ab-initio simulations. \\ \\ [1] J.-H. Kim et al., Phys. Rev. Lett. {\bf 107}, 097401 (2011).\\ [2] N. Hur et al., Nature {\bf 429}, 392 (2004).\\ [3] N. Lee et al., Phys. Rev. Lett. {\bf 110}, 137203 (2013). [Preview Abstract] |
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