Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session K5: Frustrated Magnetism: SpinelsFocus
|
Hide Abstracts |
Sponsoring Units: GMAG DMP Chair: Daniel Khomskii, University of Cologne Room: 301 |
Wednesday, March 16, 2016 8:00AM - 8:36AM |
K5.00001: From Spin Glass to Spin Liquid Ground States in Pyrochlore Molybdates Invited Speaker: Lucy Clark Magnetic pyrochlores continue to generate intense interest due to the wealth of interesting behaviours that they can display as a result of their highly frustrated nature. Here we will present our study of the molybdate pyrochlore Lu$_2$Mo$_2$O$_7$, which contains non-magnetic Lu$^{3+}$ and an antiferromagnetic network of corner-sharing tetrahedra of Mo$^{4+}$ $4d^2$ $S=1$ ions [$1$]. Magnetic susceptibility data show that Lu$_2$Mo$_2$O$_7$ enters an unconventional spin glass state at $T_f{\sim}16$ K that displays a quadratic dependence of the low temperature magnetic heat capacity, akin to that observed for its well-studied sister compound Y$_2$Mo$_2$O$_7$ [$2$]. This spin glass transition is also clearly marked in our inelastic (CNCS, SNS) and diffuse elastic magnetic (D7, ILL) neutron scattering data. Furthermore, we will show that it is possible to topochemically substitute the oxide, O$^{2-}$, ions within Lu$_2$Mo$_2$O$_7$ for nitride, N$^{3-}$, to produce an oxynitride molybdate pyrochlore of composition Lu$_2$Mo$_2$O$_5$N$_2$. Magnetic susceptibility measurements confirm that strong antiferromagnetic correlations persist within the oxynitride, which contains Mo$^{5+}$ $4d^1$ $S={\frac{1}{2}}$ ions and is thus a prime candidate to host exotic quantum spin liquid behavior. We will discuss how the enhanced quantum spin fluctuations in Lu$_2$Mo$_2$O$_5$N$_2$ appear to suppress the spin freezing transition observed in its parent oxide and instead support the formation of a gapless spin liquid phase that displays a linear dependence of the low temperature magnetic heat capacity [$3$]. [$1$] L. Clark {\textit{et al.}}, J. Solid State Chem. {\textbf{203}}, $199$ ($2013$), [$2$] H. J. Silverstein {\textit{et al.}}, Phys. Rev. B {\textbf{89}}, $054433$ ($2014$), [$3$] L. Clark {\textit{et al.}}, Phys. Rev. Lett. {\textbf{113}}, $117201$ ($2014$). [Preview Abstract] |
Wednesday, March 16, 2016 8:36AM - 8:48AM |
K5.00002: Observation of a new incommensurate phase in the spinel MnV2O4 Gilberto de la Pena Munoz, Sangjun Lee, Samuel Gleason, Taylor Byrum, Xinyue Fang, Shih-Chang Weng, Peter Abbamonte Using x-ray scattering, we studied the temperature dependence of a large volume of reciprocal space in a MnV2O4 spinel crystal. In addition to the known cubic to tetragonal phase transition at around 56 K, we observed previously unreported incommensurate modulation peaks at delta q = 0.33 0.33 -0.16. We measured the temperature dependence of these modulations and, while they exhibit a shift or splitting in momentum space analogous to that of the structural phase transition, they do so at higher temperature than the Bragg reflections (~100K). Our results suggest that MnV2O4 has an additional phase transition that may a precursor for the V t2g orbital ordering, which is closely related to the cubic to tetragonal transition. [Preview Abstract] |
Wednesday, March 16, 2016 8:48AM - 9:00AM |
K5.00003: \textbf{Geometric Magnetic Frustration in Li}$_{\mathrm{\mathbf{3}}}$\textbf{Mg}$_{\mathrm{\mathbf{2}}}$\textbf{OsO}$_{\mathrm{\mathbf{6}}}$\textbf{ Studied with Muon Spin Relaxation} J. P. Carlo, S. Derakhshan, J. E. Greedan Geometric frustration manifests when the spatial arrangement of ions inhibits magnetic order. Typically associated with antiferromagnetically (AF)-correlated moments on triangular or tetrahedral lattices, frustration occurs in a variety of structures and systems, resulting in rich phase diagrams and exotic ground states. As a window to exotic physics revealed by the cancellation of normally dominant interactions, the research community has taken great interest in frustrated systems. One family of recent interest are the rock-salt ordered oxides A$_{\mathrm{5}}$BO$_{\mathrm{6}}$, in which the B sites are occupied by magnetic ions comprising a network of interlocked tetrahedra, and nonmagnetic ions on the A sites control the B oxidation state through charge neutrality. Here we will discuss studies of Li$_{\mathrm{3}}$Mg$_{\mathrm{2}}$OsO$_{\mathrm{6}}$ using muon spin relaxation ($\mu $SR), a highly sensitive local probe of magnetism. Previous studies of this family included Li$_{\mathrm{5}}$OsO$_{\mathrm{6}}$, which exhibits AF order below 50K with minimal evidence for frustration, and Li$_{\mathrm{4}}$MgReO$_{\mathrm{6}}$, which exhibits glassy magnetism. Li$_{\mathrm{3}}$Mg$_{\mathrm{2}}$RuO$_{\mathrm{6}}$, meanwhile, exhibits long-range AF, with the ordering temperature suppressed by frustration. But its isoelectronic twin, Li$_{\mathrm{3}}$Mg$_{\mathrm{2}}$OsO$_{\mathrm{6}}$ (5$d^{\mathrm{3}}$ vs. 4$d^{\mathrm{3}})$ exhibits very different behavior, revealed by $\mu $SR to be a glassy ground state below 12K. Understanding why such similar systems exhibit diverse ground-state behavior is key to understanding the nature of geometric magnetic frustration. [Preview Abstract] |
Wednesday, March 16, 2016 9:00AM - 9:12AM |
K5.00004: Effects of Zn doping on the A-Site antiferromagnet spinel CuRh$_{2}$O$_{4}$ Alexander Zakjevskii, Dalmau Reig-i-Plessis, Alexander Thaler, Ashfia Huq, Gregory MacDougall A major recent focus of the correlated electron community has been the investigation of 4d and 5d transition metal oxides, which are predicted to have novel phases arising from relativistic spin-orbit coupling. We have recently synthesized and characterized several compounds of the doped spinel series Cu$_{1-x}$Zn$_{x}$Rh$_{2}$O$_{4}$. The parent compound is a normal spinel which undergoes a cubic-tetragonal structural phase transition at T$\sim$850K, and further undergoes a suspected antiferromagnetic transition at T$_{N}$=22K. We have performed powder x-ray and neutron diffraction, and bulk magnetization measurements on members of the Zn-doping series. Magnetization measurements clearly indicate a monotonic suppression of the N\'{e}el temperature with increasing Zn content, to a quantum critical point at x$\cong$0.42. X-ray results indicate a change in structure occurring near the same doping. We will present these data and discuss the results within the context of exotic predictions in the literature. Lastly, we will discuss our recent neutron powder diffraction measurements and insights gleaned about the local spin state. [Preview Abstract] |
Wednesday, March 16, 2016 9:12AM - 9:24AM |
K5.00005: Magnetic Ordering in FeSc2S4 K.W. Plumb, J.R. Morey, J.P.C. Ruff, J.A. Rodriguez-Rivera, T.M. McQueen, S.M. Koohpayeh, C.L. Broholm FeSc2S4 is a cubic spinel where orbitally active Fe$^{2+}$ ions occupy the A-site diamond sublattice. Despite a high spin (S=2) state and Curie Weiss temperature of 45~K thermodynamic measurements show no indication of a phase transition and the material has been proposed as a unique example of a spin-orbital liquid. This ground state might arise from competition between on site spin-orbit coupling and Kugel-Khomskii exchange. We report neutron scattering measurements on polycrystalline samples of FeSc2S4 which bring this picture into question. They reveal a previously unreported magnetically ordered state below 11 K. No structural distortions are visible with neutron or x-ray scattering. The effect of hydrostatic pressure on the magnetic excitation spectrum was also explored and found to be minimal. [Preview Abstract] |
Wednesday, March 16, 2016 9:24AM - 9:36AM |
K5.00006: Quantum phase transitions and anomalous Hall effect in a pyrochlore Kondo lattice Sarah Grefe, Wenxin Ding, Qimiao Si The metallic variant of the pyrochlore iridates Pr$_{\mathrm{2}}$Ir$_{\mathrm{2}}$O$_{\mathrm{7}}$ has shown characteristics of a possible chiral spin liquid state [PRL \textbf{96} 087204 (2006), PRL \textbf{98}, 057203 (2007), Nature \textbf{463}, 210 (2010)] and quantum criticality [Nat. Mater. \textbf{13}, 356 (2014)]. An important question surrounding the significant anomalous Hall response observed in Pr$_{\mathrm{2}}$Ir$_{\mathrm{2}}$O$_{\mathrm{7}}$ is the nature of the f-electron local moments, including their Kondo coupling with the conduction d-electrons. The heavy effective mass and related thermodynamic characteristics indicate the involvement of the Kondo effect in this system's electronic properties. In this work, we study the effects of Kondo coupling on candidate time-reversal-symmetry-breaking spin liquid states on the pyrochlore lattice. Representing the f-moments as slave fermions Kondo-coupled to conduction electrons, we study the competition between Kondo-singlet formation and chiral spin correlations and determine the zero-temperature phase diagram. We derive an effective chiral interaction between the local moments and the conduction electrons and calculate the anomalous Hall response across the quantum phase transition from the Kondo destroyed phase to the Kondo screened phase. We discuss our results' implications for Pr$_{\mathrm{2}}$Ir$_{\mathrm{2}}$O$_{\mathrm{7}}$ and related frustrated Kondo-lattice systems. [Preview Abstract] |
Wednesday, March 16, 2016 9:36AM - 9:48AM |
K5.00007: Chemical insights into the synthesis and properties of polycrystalline and single crystal iron scandium sulfide (FeSc$_{\mathrm{2}}$S$_{\mathrm{4}})$ Jennifer R. Morey, Kemp W. Plumb, Seyed M. Koohpayeh, Collin L. Broholm, Tyrel M. McQueen Iron scandium sulfide, FeSc$_{\mathrm{2}}$S$_{\mathrm{4}}$, has recently attracted significant theoretical and experimental interest as a candidate spin-orbital liquid. An AB$_{\mathrm{2}}$X$_{\mathrm{4}}$ spinel, FeSc$_{\mathrm{2}}$S$_{\mathrm{4}}$ (space group Fd-3m, No. 227) features a high degree of frustration associated with the Fe$^{\mathrm{2+}}$, which occupies the A-site diamond sublattice and is tetrahedrally coordinated by sulfur. The Fe$^{\mathrm{2+}}$ ion is in a high spin (S$=$2) state, resulting in orbital degeneracy due to a single hole on the $e$ orbitals. We report the strides we have made to produce material in powder and single crystal form, and the relationship between the chemistry and the structural, magnetic, and thermodynamic properties of FeSc$_{\mathrm{2}}$S$_{\mathrm{4}}$. [Preview Abstract] |
Wednesday, March 16, 2016 9:48AM - 10:00AM |
K5.00008: Weyl Magnon Fei-Ye Li, Yao-Dong Li, Yue Yu, Yong Baek Kim, Leon Balents, Gang Chen Conventional magnetic orders in Mott insulators are often believed to be trivial as they are simple product states. In this talk, we argue that this belief is not always right. We study a realistic spin model on the breathing pyrochlore lattice. We find that, although the system has a magnetic ordered ground state, the magnetic excitation is rather nontrivial and supports linear band touchings in its spectrum. This linear band touching is a topological property of the magnon band structure and is thus robust against small perturbation. We thus name this magnon band touching as “Weyl magnon”. Just like the Weyl fermion, the existence of Weyl magnon suggests the presence of chiral magnon surface states. Unlike the surface Fermi arcs for the Weyl fermions, the chiral surface state for Weyl magnon appears at a finite energy due to the bosonic nature of the magnons. Moreover, the external magnetic field only couples to the spins with a Zeeman term and thus can readily shift the Weyl node position. This provides a way to control the Weyl magnon. Our work will inspire a re-examination of the excitation spectrum of many magnetic ordered systems. [Preview Abstract] |
Wednesday, March 16, 2016 10:00AM - 10:12AM |
K5.00009: Spin Glass Behavior and Field Induced Anisotropic Magnetic Ordering in S $=$ 2 Frustrated Spinel GeFe2O4 Tao Zou, Zhiling Dun, Tao Hong, Huibo Cao, Clarina dela Cruz, Michael Gottschalk, Mengze Zhu, Haidong Zhou, Xianglin Ke We report comprehensive studies of magnetic properties of spinel GeFe2O4 by means of magnetic susceptibility and heat capacity measurements on both polycrystalline and single crystalline samples as well as neutron powder diffraction measurements. We find that this system shows a spin-glass ground state with the transition temperature around T \textasciitilde 21 K, in contrast to the static antiferromagnetic order reported in earlier literature. In addition, we reveal a field-induced magnetic ordering, which displays strong magnetic anisotropy character. [Preview Abstract] |
Wednesday, March 16, 2016 10:12AM - 10:24AM |
K5.00010: Orbital degeneracy near the itinerant electron limit in CoV2O4 D. Reig-i-Plessis, D. Casavant, V. O. Garlea, A. A. Aczel, M. Feygenson, J. Neuefeind, H. D. Zhou, S. E. Nagler, G. J. MacDougall Vanadium spinels, AV$_2$O$_4$ have both magnetic frustration and orbital degeneracy on the V$^{3+}$ sublattice, which lead to strong coupling of the orbital, lattice and spin degrees of freedom. Additionally, upon decreasing the V-V distance, the material is predicted to go from a Mott insulator to a metallic phase. Of all the materials in the AV$_2$O$_4$ series, CoV$_2$O$_4$ is closest to the predicted transition, and it's debated whether it may be fully described by either localized or itinerant electrons pictures. In all other studied vanadium spinels, there is a cubic to tetragonal transition associated with ordering of the degenerate V$^{3+}$ orbitals, consistent with a local orbital picture but, this transition is surprisingly absent from CoV$_2$O$_4$ despite being an insulator with local spins. In this talk we present recent high resolution neutron diffraction and inelastic scattering measurements by our group on powders of CoV$_2$O$_4$. Diffraction data show there is small but clear first order structural transition present which correlates with canting of the V$^{3+}$ spins, while inelastic data are well described by a local spinwave picture. We discuss how these results contribute evidence of a local orbital ordering phase in the region near electron itinerancy. [Preview Abstract] |
Wednesday, March 16, 2016 10:24AM - 10:36AM |
K5.00011: Spin Dynamics and Two-Dimensional Correlations in the FCC Antiferromagnetic Sr$_2$YRuO$_6$ Steven Disseler, J. W. Lynn, R. F. Jardim, M. S. Torikachvili, E. GR The face-centered cubic lattice lattice of Ru$^{5+}$ spins in the double perovskite Sr$_{2}$YRuO$_{6}$ shows a delicate three dimensional antiferromagnetic (AFM) ground state composed of stacked square AFM layers. We present new inelastic neutron scattering data taken on this state revealing a gapped low-energy excitation band that may be modeled by a simple $J_1-J_2$ interaction scheme allowing quantitative comparison of similar materials. At higher temperatures, the low-energy excitation spectrum is dominated by a quasi-elastic component associated with size fluctuations of two-dimensional AFM clusters that exhibit asymmetric correlations even at low temperatures. Thus, the FCC lattice in general and the double perovskite structure in particular emerge as hosts of both two-dimensional and three-dimensional dynamics resulting from frustration. [Preview Abstract] |
Wednesday, March 16, 2016 10:36AM - 10:48AM |
K5.00012: Unanticipated spin gap measured in the frustrated quasi-FCC $d^3$ double perovskites $La_2LiXO_6$ (X = Ru, Os) Dalini D Maharaj, Gabriele Sala, Casey A Marjerrison, John Greedan, Bruce Gaulin, Matthew Stone There is much current interest in the influence of strong spin-orbit (SO) interactions on exotic ground state selection in new 4d and 5d magnets, particularly involving 4d$^5$ Ir. Here we consider double perovskites of the form $A_2BB'O_6$ which are based on heavy 4d or 5d magnetic ions, where the SO interaction is expected to be significant as it increases as $\sim Z^4$. The double perovskite structure can accommodate a variety of magnetic ions on the B' site, providing a playground for systematic studies of the exotic ground states stabilized by strong SO coupling. Here, we report inelastic neutron scattering (INS) measurements conducted on the frustrated monoclinic magnets, La$_2$LiXO$_6$ (X = Ru, Os), wherein the magnetic moments decorate a quasi face-centered-cubic lattice. Our results show the development of a spin gap in the spin excitation spectrum of size $\Delta_{Os}$ = 8 meV and $\Delta_{Ru}$ = 2.5meV concomitant with $T_N$, which is unexpected for orbitally quenched $d^3$ systems. We liken these results to INS results obtained for Ba$_2$YXO$_6$ and La$_2$NaXO$_6$, which were also shown to exhibit spin gaps that correlate with $T_N$. We shall discuss trends observed in these three d$^3$ double perovskite families which correlate strong SO coupling, spin gap and T$_N$. [Preview Abstract] |
Wednesday, March 16, 2016 10:48AM - 11:00AM |
K5.00013: Raman spectroscopy study of spin-orbital liquid candidate FeSc$_2$S$_4$ Streit Cunningham, K.W. Plumb, J.R. Morey, T.M. McQueen, S. Koohpayeh, C.L. Broholm, Natalia Drichko The A-site cubic spinel FeSc$_2$S$_4$, containing Fe$^{2+}$ ions in a tetrahedral S$_4$ environment, represents a rare candidate of a spin-orbital liquid, where spin and orbital order remain suppressed down to the lowest measurable temperature [1]. We studied phonon spectrum and orbital excitations in FeSc$_2$S$_4$ by Raman spectroscopy on single crystals. At temperatures below 100K we observe widening of sulfur 330 cm$^{-1}$ T$_{2g}$ and 365 cm$^{-1}$ A$_{1g}$ phonon modes with an additional weak mode emerging at 400 cm$^{-1}$. These changes can indicate weak lattice distortions associated with the sulfur sites. Below 100K we also observe orbital excitations at frequencies of approximately 2000 cm$^{-1}$. We discuss the result in terms of a competition of spin-orbital liquid and a magnetically ordered state. [1] L. Mittelstadt et al., Phys. Rev. B 91 125112 (2015). [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700