Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session R6: Frustrated Magnetism: Triangular Lattice MagnetsFocus
|
Hide Abstracts |
Sponsoring Units: GMAG DMP Chair: Collin Broholm, Johns Hopkins University Room: 302 |
Thursday, March 17, 2016 8:00AM - 8:36AM |
R6.00001: Frustrated quantum magnetism in the 6H-perovskites Invited Speaker: Jeffrey Quilliam I will review the recent state of research on the 6H-perovskites, Ba$_3$MA$_2$O$_9$, a large class of materials that can accommodate many different magnetic ions on ostensibly triangular lattices. This class of materials has given rise to several important discoveries in recent years, including quantum spin liquids, a quantum spin-orbital liquid and the first perfectly triangular spin-1/2 antiferromagnet. Many of these materials also provide an interesting interplay of magnetic, orbital and charge degrees of freedom. Others suffer from high levels of site disorder, which leads to interesting physics, at least in the case of the spin-orbital liquid candidate Ba$_3$CuSb$_2$O$_9$. I will primarily discuss our recent work on the materials Ba$_3$MSb$_2$O$_9$, where M = Cu, Ni and Co using the techniques of nuclear magnetic resonance (NMR), muon spin rotation ($\mu$SR) and ultrasound velocity measurements. [Preview Abstract] |
Thursday, March 17, 2016 8:36AM - 8:48AM |
R6.00002: Spin glassy behaviors and isolated spin dimers in \textit{BaCr}$_{9p}$\textit{Ga}$_{12}_{-}_{9p}O_{19}$ Junjie Yang, Anjana Samarakoon, Kyun Woo Hong, Seung-Hun Lee, John R. D. Copley, Qingzhen Huang, Taku J Sato Theoretical results suggested that quantum fluctuations may induce glassy states (spin jam states) in defect-free spin systems. Recently our experimental results indicated the existence of spin jam states in SrCr$_{9}_{p}$Ga$_{12-9}_{p}$O$_{19}$ (SCGO($p))$ in which the Cr$^{3+}$ ions form two-dimensional (2D) triangular lattice of bi-pyramids. Here we report a isostructural new system BaCr$_{9}_{p}$Ga$_{12-9}_{p}$O$_{19}$ (BCGO($p))$ with 0.4\textless $p$\textless 0.9. Neutron diffraction results show that BCGO($p)$ is isostructural as SCGO($p)$ but with a larger $c $lattice indicating that BCGO($p)$ is more 2D. BCGO($p)$ exhibits similar glassy behaviors as SCGO($p)$ but with higher freezing temperature. Very high Curie-Weiss temperature and frustration index were also observed in BCGO($p)$ suggesting that BCGO($p)$ is one of the most frustrating system. Inelastic neutron scattering results show that BCGO($p)$ has dispersionless magnetic excitations at an energy of 16.5(1) meV arising from 4$f_{vi}$-4$f_{vi}$ spin dimers. These spin dimers are adjacent spins in neighboring triangular lattice planes which separate the 2D interacting triangular lattice of bi-pyramids. These results indicate that BCGO($p)$ is a new good candidate for studying spin jam states. [Preview Abstract] |
Thursday, March 17, 2016 8:48AM - 9:00AM |
R6.00003: Muon spin rotation study of spin dimers on a triangular lattice in Ba3MRu2O9. Djamel ZIAT, Aimé Verrier, Jeffrey Quilliam, Adam Aczel, Ryan Sinclair, Qiang Chen, Haidong Zhou The family of hexagonal perovskites, Ba3MA2O9 has recently been proven to be fertile ground for the discovery of new, exotic magnetic phases, including several quantum spin liquid candidates. The 6H-perovskites can also accommodate spin dimers on a triangular lattice, as in the ruthenate materials Ba3MRu2O9. We will present measurements on materials containing M3$+$ (M $=$ Y, La, Lu, In), which give rise to mixed valence Ru4.5$+$ ions wherein the orbital and charge degrees of freedom must also be considered. In particular, muon spin rotation (\textmu SR) experiments, have allowed us to probe the nature of the magnetically ordered ground state of these materials at low temperatures. [Preview Abstract] |
Thursday, March 17, 2016 9:00AM - 9:12AM |
R6.00004: Magnetic Correlations in the Triangular Antiferromagnet TbInO$_3$ Gabriele Sala, Lucy Clark, Dalini Maharaj, Matthew B. Stone, Kevin S. Knight, Sang-Wook Cheong, Bruce D. Gaulin TbInO$_3$ crystallizes with a hexagonal $P6_3cm$ structure in which layers of edge-sharing triangles of magnetic Tb$^{3+}$ ions are separated by non-magnetic [InO$_5$]$^{7-}$ units. TbInO$_3$, therefore, realizes an excellent opportunity to explore the behavior of a two-dimensional magnetic triangular lattice, a canonical model of geometric frustration. Here we present our study of a polycrystalline sample of TbInO$_3$. Our high resolution powder neutron diffraction data (HRPD, ISIS) of TbInO$_3$ confirm that the triangular layers of Tb$^{3+}$ remain undistorted to at least $0.46$ K. Magnetic susceptibility data follow Curie-Weiss behavior over a wide range of $T$ with ${\theta}=-17.19(3)$ K indicating the dominance of antiferromagnetic correlations. The susceptibility data also show an absence of conventional long-range spin order down to at least $0.55$ K, reflecting the frustrated nature of TbInO$_3$. Elastic magnetic diffuse neutron scattering (SEQUOIA, SNS) is observed below ${\sim}15$ K, due to the presence of static two-dimensional spin correlations. The spectrum of crystal field excitations in TbInO$_3$ appears to have an exotic form due to the existence of two crystallographically distinct Tb$^{3+}$ sites and leads to a strong Ising anisotropy of the spin symmetry. [Preview Abstract] |
Thursday, March 17, 2016 9:12AM - 9:24AM |
R6.00005: ABSTRACT WITHDRAWN |
Thursday, March 17, 2016 9:24AM - 9:36AM |
R6.00006: A spin-orbit coupled triangular lattice quantum spin liquid in YbMgGaO4: a semiclassical study Yao-Dong Li, Gang Chen Recently YbMgGaO4 is proposed to be the first strong spin-orbit coupled quantum spin liquid candidate system that contains odd number of electron per unit cell with effective spin 1/2 local moments. In this talk we analyze the classical phase diagram of the most generic model that describes the Yb effective spin 1/2 local moments on the triangular lattice. We show the frustration is strong near the phase boundary between the 120 degree state and the stripe ordered phase. Further, we study the quantum fluctuation of the spin momentum by the linear spin wave theory and find that the magnetic order is destroyed in the strongly frustrated regimes of the phase diagram. Our result is compatible with the experimental results that suggest a quantum spin liquid ground state. [Preview Abstract] |
Thursday, March 17, 2016 9:36AM - 9:48AM |
R6.00007: Magnetic Ground State of the Ideal Triangular-Lattice Antiferromagnets Tuned by the Inter-layer Interactions Jie Ma, M Matsuda, Y. Kamiya, Z. L. Dun, C. dela Cruz, C. D. Batista, Y. Qiu, N Butch, J. R. D. Copley, H. D. Zhou Neutron inelastic scattering and diffraction techniques have been applied to investigate both structures and spin wave excitations of the tri-perovskite Ba$_{\mathrm{3}}$\textit{MM'}$_{\mathrm{2}}$O$_{\mathrm{9}}$, which is antiferromagnetic with the equilateral-triangular lattice M layers. Although the magnetic structure of the system is non-collinear 120\textdegree in ab-plane, the c-axis canting appears by increasing the spin momentum from $S$(Co$^{\mathrm{2+}}) \quad =$ 1/2 to $S$(Mn$^{\mathrm{2+}}) \quad =$ 5/2. Our measurements clearly show that the magnetic ground state and excitations could be modified by the inter-layer interaction, which is strongly interfered by the type and staggering method of the nonmagnetic $M'$O6 clusters. In addition, the lattice-related quantum phenomena were discussed, such as the temperature-dependent acoustic mode in Ba3NiNb2O9, and the pressure-effect on the magnetic dynamics of the Fermi-liquid-like ground state, Ba3NiSb2O9(6H-B). [Preview Abstract] |
Thursday, March 17, 2016 9:48AM - 10:00AM |
R6.00008: An indirect RIXS study of roton excitation in triangular lattice antiferromagnet Trinanjan Datta, Cheng Luo, Dao-Xin Yao The antiferromagnetic triangular lattice is characterized by the presence of roton excitations. We propose that the K-edge indirect resonant inelastic x-ray scattering (RIXS) spectrum of a triangular lattice antiferromagnet can serve as a novel spectroscopic tool to detect the presence of roton excitations. By considering self-energy corrections to the spin-wave spectrum and magnon decay rates in its ordered coplanar three-sublattice 120 degree magnetic state, we find that a single-peak RIXS spectrum forms at the roton momentum, Luo et. al. Phys. Rev. B 92, 035109 (2015). The single peak feature is in sharp contrast to the other high symmetry points where the RIXS spectrum splits into a multipeak structure. It is this contrast which can be utilized as an experimental signature to detect the presence of rotons. We also investigate the effect of XXZ spin anisotropy, orthorhombic spatial anisotropy, and DM interaction in the triangular lattice and find that the roton peak is affected. [Preview Abstract] |
Thursday, March 17, 2016 10:00AM - 10:12AM |
R6.00009: 2D Heisenberg Triangular Antiferromagnet in Ba$_3$CoSb$_2$O$_9$ Alun Biffin, Franz Demmel, Helen Walker, Michael Hayward, Radu Coldea We present inelastic neutron scattering (INS) experiments on the triangular antiferromagnet (TAF) Ba$_3$CoSb$_2$O$_9$. High energy INS measurements allowed the crystal field levels of Co$^{2+}$ ions to be resolved, and subsequently the terms relevant to its single ion Hamiltonian to be derived with the conclusion that the ions have a $J_\text{eff}=1/2$ doublet as their groundstate with relatively weak local trigonal distortion of CoO$_6$ octahedra. The result is a system which is a rare realisation of the canonical spin 1/2 Heisenberg TAF. Following this, low energy, high-resolution INS experiments have been performed which reveal the spin wave excitations emanating from the 120$^{\circ}$ ordered phase below $T_\text{N}=3.8$K. However, as will be seen, linear spin wave calculations are not sufficient to describe all the features of the data, and these anomalies hint at quantum dynamics beyond linear spin wave theory within this realisation of the canonical $S$=1/2 TAF system. [Preview Abstract] |
Thursday, March 17, 2016 10:12AM - 10:24AM |
R6.00010: Quantum phase transitions in triangular lattice Heisenberg anti-ferromagnet in a magnetic field Mengxing Ye, Andrey Chubukov We present the zero temperature phase diagram of a large $S$ Heisenberg anti-ferromagnet on a frustrated triangular lattice with the nearest neighbor ($J_1$) and the next nearest neighbor ($J_2$) interactions, in a magnetic field. We show that the classical model has an “accidental” degeneracy for all $J_2/J_1$ and all fields below the saturation field, which gives rise to the extended manifold of the ground state spin configurations. Quantum fluctuations, however, lift this degeneracy. For small $J_2/J_1$, they select one of three different co-planar states, depending on the field value. We argue that above some critical ratio of $J_2/J_1$, which weakly depends on a magnetic field, these fluctuations select the stripe phase. We analyze in detail the mechanism of the selection of the stripe phase and explore the nature of the quantum phase transition in a magnetic field between the ordered phases as $J_2/J_1$ passes through a critical value. [Preview Abstract] |
Thursday, March 17, 2016 10:24AM - 10:36AM |
R6.00011: Neutron diffraction study of low dimensional magnetic system: single crystal $\alpha $-NaMnO$_{\mathrm{2}}$ Rebecca Dally, Stephen Wilson, Jeffrey Lynn, Robin Chisnell, Leland Harriger, Michael Graf $\alpha -$NaMnO$_{\mathrm{2}}$ contains complex, low dimensional interactions and is magnetically frustrated due to the triangular arrangement of Mn$^{\mathrm{3+}}$ (S$=$2, t$_{\mathrm{2g}}^{\mathrm{3}}$e$_{\mathrm{g}}^{\mathrm{1}})$ atoms in the crystal. Nearest neighbor Mn atoms lie along the $b$-axis in a chain; these chains span the ab-plane, where a mean-field approach to the interchain exchange predicts the cancellation of interactions, giving rise to quasi-1D behavior. Here we will present the results of our recent single crystal neutron diffraction measurements of correlated spin behavior in this Na$_{\mathrm{x}}$MnO$_{\mathrm{2}}$. A complex evolution of the ordering wave vector, spin anisotropy, and dimensionality is observed as the system approaches the antiferromagnetic phase transition. The implications for the inherent dimensionality of this system and its coupling to the lattice will be discussed. [Preview Abstract] |
Thursday, March 17, 2016 10:36AM - 10:48AM |
R6.00012: Giant magnon-phonon coupling in LiCrO2 Sándor Tóth, Katharina Rolfs, Björn Wehinger, Turan Birol, Uwe Stuhr, Björn Fåk, Kenta Kimura, Hiroshi Takatsu, Christian Rüegg The study of low dimensional and frustrated quantum magnets has been a central problem in condensed matter physics over the past decades. The main feature of frustrated magnets is the macroscopic degeneracy of the ground state that can be lifted by weak additional effects such as quantum fluctuations. This can lead to new exotic ground states without long-range order and novel excitations. Here we present an example, LiCrO$_2$, where frustration (and electronic properties) leads to strong coupling between magnons and phonons in a triangular lattice antiferromagnet. This coupling leads to a novel magnon dispersion with a roton minima at the zone boundary [1]. We show direct evidence using inelastic neutron and X-ray scattering that the roton is the direct result of the magnon-phonon coupling. Furthermore the discovered effect could shed light on the underlying physics of other Cr$^{3+}$ compounds with strange properties, such as the observed flat magnetic modes in the pyrochlore lattice antiferromagnet MgCr$_2$O$_4$. [1] S. Toth, et al., PRL 109, 127203 (2012). [Preview Abstract] |
Thursday, March 17, 2016 10:48AM - 11:00AM |
R6.00013: Nanosized helical magnetic domains in strongly frustrated Fe$_3$PO$_4$O$_3$ Mitchell Bordelon, Kate Ross, Greg Terho, James Neilson Non-centrosymmetric Fe$_3$PO$_4$O$_3$ (space group $R3m$) contains triangular motifs of Fe$^{3+}$ ions coupled by strong antiferromagnetic interactions ($|\Theta_{CW}| > 900$ K). Neutron powder diffraction below $T_N = 163$ K reveals the formation of an ordered helical incommensurate magnetic structure, with helical axis in the hexagonal $ab$ plane and modulation length of $\sim$ 100 Å. The magnetic structure forms needle-like correlation volumes perpendicular to the $ab$ plane that extend at least to 900 Å along the $c$-axis, but are confined to $\sim$ 70 Å in the $ab$ plane. The refined magnetic moment, supported by magnetization measurements of a magnetically diluted series (Fe$_{3-x}$Ga$_x$PO$_4$O$_3$), indicates a reduced Fe$^{3+}$ moment, suggesting metal-ligand charge transfer. High-resolution synchrotron X-ray diffraction reveals no lattice symmetry change below $T_N$. Absence of long-range in-plane order below $T_N$ signifies the formation of a high density of defects in the magnetic structure. The defect-rich helical magnetic phase in Fe$_3$PO$_4$O$_3$ offers insight into the stabilization of topological spin textures in antiferromagnets. [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