Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session A51: Coupled Frustrated Sub-UnitsFocus Recordings Available
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Sponsoring Units: GMAG DMP Chair: Christianne Beekman, Florida State Univ. Room: McCormick Place W-474B |
Monday, March 14, 2022 8:00AM - 8:12AM |
A51.00001: Understanding magnetic properties of the Breathing Pyrochlore Material Ba3Yb2Zn5O11 Sachith E Dissanayake, Zhenzhong Shi, William M Steinhardt, Jeffrey G Rau, Han Yan, Rabindranath Bag, Nicholas Butch, Matthias D Frontzek, Andrey Podlesnyak, David E Graf, Eun Sang Choi, Franz Lang, Stephen J Blundell, Andriy H Nevidomskyy, Michel J P Gingras, Sara Haravifard Breathing pyrochlore systems are composed of corner-sharing tetrahedra of different sizes pointing in opposing directions, leading to different intra- and inter-tetrahedra exchange interactions and the emergence of the Dzyaloshinskii-Moriya interaction due to loss of inversion symmetry. Ba3Yb2Zn5O11 is unique among breathing pyrochlore compounds for being in the nearly decoupled limit, where inter-tetrahedra interactions are weak. In this talk, we will discuss the magnetic properties in this material and present our results collected on a single crystal sample. We will discuss the features that agree with the single tetrahedron model and a possible scenario for the deviation of the experimental observation from the single tetrahedron model. |
Monday, March 14, 2022 8:12AM - 8:24AM |
A51.00002: Neutron Scattering Studies of new RE Breathing Pyrochlore compound: Ba3Tm2Zn5O11 Lalit Yadav, Rabindranath Bag, Sachith E Dissanayake, Guangyong Xu, Craig Brown, Nicholas Butch, Franz Lang, Stephen J Blundell, Adam A Aczel, Yan Wu, Alexander I Kolesnikov, Sara Haravifard, Zhenzhong Shi Breathing Pyrochlore materials have emerged as a promising candidate to study frustrated magnetism and topological phenomena, such as Weyl and Dirac magnons. We have synthesized a new member in the rare-earth based family of Breathing Pyrochlore compounds: Ba3Tm2Zn5O11. We have grown the single crystal of this compound. We have characterized its thermodynamic properties, which show no sign of ordering down to the lowest accessible temperature. Further, we have performed inelastic neutron scattering on single crystals to study the low-energy magnetic excitations. We have also performed high-resolution neutron diffraction at multiple fields and temperatures to study the field-driven transitions. In this talk, we are going to present our latest experimental results for this new member of the RE-based breathing pyrochlore compound Ba3Tm2Zn5O11. |
Monday, March 14, 2022 8:24AM - 8:36AM |
A51.00003: Hierarchical excitations from correlated spin tetrahedra on the breathing pyrochlore lattice Shang Gao, Andrew F May, Maohua Du, Joseph Paddison, Hasitha Suriya Arachchige, Ganesh Pokharel, Clarina R Dela Cruz, Qiang Zhang, Georg Ehlers, David S Parker, David G Mandrus, Matthew B Stone, Andrew Christianson The hierarchy of the coupling strengths in a physical system often engenders an effective model at low energies where the decoupled high-energy modes are integrated out. Here, using neutron scattering, we show that the spin excitations in the breathing pyrochlore lattice compound CuInCr4S8 are hierarchical and can be approximated by an effective model of correlated tetrahedra at low energies. At higher energies, intra-tetrahedron excitations together with strong magnon-phonon couplings are observed, which suggests the possible role of the lattice degree of freedom in stabilizing the spin tetrahedra. Our work illustrates the spin dynamics in CuInCr4S8 and demonstrates a general effective cluster approach to understand the dynamics on the breathing-type lattices. |
Monday, March 14, 2022 8:36AM - 8:48AM |
A51.00004: Time evolution of metastable magnetic configurations in the geometrically frustrated spin-chain compound Ca3Co2O6 Leonardo Civale, Ivan Nekrashevich, Vivien Zapf Ca3Co2O6 exhibits rich magnetic phenomena originating in its crystal structure. Due to the ferromagnetic coupling between Co atoms along the crystallographic c-axis, it forms spin chains along this direction. In the ab-plane, however, these chains form triangular lattice which, in conjunction with the antiferromagnetic intra-chain interaction, produces geometric frustration. At low temperatures and for H parallel to the spin chains, the equilibrium state above a critical field Hc=3.6T is the fully aligned state characterized by a saturation magnetization Msat. Below Hc, the ground state is the ordered state with two chains magnetized along H and one chain in the opposite direction, resulting in M=Msat/3. However, isothermal M(H) curves exhibit a complex hysteretic behavior with steps that indicate the existence of metastable configurations. In the lower (increasing H) branch of the M(H) loop, one step at Hc has M higher than Msat/3, showing that there is an energy barrier precluding the decay of the metastable state to the ground state. We investigated the slow time evolution of the magnetization, M(t), in the metastable states. The evolution is not exponential, consistent with interacting objects, and in large portions of the T-H diagram M(t) is well described by the logarithmic law typically observed in vortex dynamics. In some T-H conditions, M(t) evolves in the direction opposite to equilibrium, hinting to the presence of hidden configurations. In some cases, M(t) evolves non-monotonically, first increasing and then decreasing, as the hidden configuration in turn evolves towards equilibrium. |
Monday, March 14, 2022 8:48AM - 9:00AM |
A51.00005: A field-induced gap observed in the metal –organic framework [(C2H5)3NH]2Cu2(C2O4)3 via specific heat measurements Charuni Dissanayake, KAMH Siddiquee, Riffat Munir, PKK Kumarasinghe, Wesley Newsome, Fernando Uribe-Romo, Yasuyuki Nakajima The coordination of metal-linkers in [(C2H5)3NH]2Cu2(C2O4)3 forms a three-dimensional hyper-honeycomb lattice. No long-range magnetic order was experimentally observed at low temperatures down to 60 mK in this material [1], suggesting an exotic magnetic ground state. We here report specific heat of the single-crystal [(C2H5)3NH]2Cu2(C2O4)3 in magnetic field at low temperatures. The magnetic contribution to the specific heat (Cmag) shows linear-in-temperature behavior in the low temperature region, and Cmag is significantly suppressed with magnetic fields. This behavior can be attributed to weakly-coupled spin-1/2 antiferromagnetic Heisenberg chains proposed by Jacko et al. [2], due to a Jahn−Teller distortion. We can also ascribe the observed field-induced gap to effective staggered fields induced by the Dzyaloshinskii- Moriya interaction in the quasi-one-dimensional chains. Our results strongly suggest that the lack of magnetic order and anomalous specific heat in [(C2H5)3NH]2Cu2(C2O4)3 are due to the quasi-one dimensional S=1/2 antiferromagnetic chains. |
Monday, March 14, 2022 9:00AM - 9:12AM |
A51.00006: Noncollinear spin structure with weak ferromagnetism in NbMnP Masaaki Matsuda, Depei Zhang, Qiang Zhang, Yoshiki Kuwata, Takahiro Sakurai, Hitoshi Ohta, Hitoshi Sugawara, Keiki Takeda, Junichi Hayashi, Hisashi Kotegawa NbMnP is a metallic material, which consists of the zigzag chains of Mn moments along the b axis. The magnetic susceptibility as well as the resistivity shows an anomaly at 233 K, which indicates an antiferromagnetic phase transition. Our neutron powder diffraction experiment reveals that the magnetic structure is a Q=0 structure and noncollinear with an easy plane anisotropy perpendicular to the b axis and the a and c axis magnetic components align antiferromagnetically and ferromagnetically along the zigzag chain direction, respectively. The ordered moment is 1.2μB, which is reduced probably due to the itineracy of the Mn moments. A localized picture model suggests that the Q=0 magnetic structure is formed by the frustration among several exchange couplings. A weak ferromagnetic component is also present in the antiferromagnetic phase, which is considered to be caused by a Dzyaloshinskii-Moriya interaction. |
Monday, March 14, 2022 9:12AM - 9:48AM |
A51.00007: Exotic high-field state in the quantum sawtooth chain material atacamite, Cu2Cl(OH)3 Invited Speaker: Leonie Heinze The key ingredient for unconventional magnetic states such as quantum spin liquids and magnetization plateaus is magnetic frustration – often encountered in systems where the local geometries and the magnetic interactions are incompatible. A unique and fascinating member among such frustrated quantum magnets is the natural mineral atacamite, Cu2Cl(OH)3 [1,2]. This compound has recently been established as material realization of the quantum sawtooth chain – a seminal model in frustrated quantum magnetism. In this system, corner-sharing spin triangles are arranged in a chain with two exchange interactions: J along the chain spine, J’ within the sawtooth triangles. In atacamite, the sawtooth chains were found to be anisotropic with J’/J ~ 1/3 [1]. |
Monday, March 14, 2022 9:48AM - 10:00AM |
A51.00008: Dynamical Signatures of Rank-2 U(1) Spin Liquids Emily Zhang, Finn Lasse Buessen, Yong-Baek Kim Emergent U(1) gauge theories and artificial photons in frustrated magnets are outstanding examples of many-body collective phenomena. The classical and quantum regimes of these systems provide platforms for classical and quantum spin liquids, and are the subject of current active theoretical and experimental investigations. Recently, realizations of rank-2 U(1) (R2-U1) gauge theories in three-dimensional frustrated magnets have been proposed. Such systems in the quantum regime may lead to the so-called fracton ordered phases -- a new class of topological order that has been associated with quantum stabilizer codes and holography. However, there exist few distinguishing characteristics of these states for their detection in real materials. Here we focus on the classical limit, and present the dynamical spin structure factor for a R2-U1 spin liquid state on a breathing pyrochlore lattice. Remarkably, we find unique signatures of the R2-U1 state, and we contrast them with the results obtained from a more conventional U(1) spin liquid. These results provide a new path of investigation for future inelastic neutron scattering experiments on candidate materials. |
Monday, March 14, 2022 10:00AM - 10:12AM |
A51.00009: Synthesis, physical and magnetic properties of CuAlCr4S8: a new Cr-based breathing pyrochlore Sudarshan Sharma, Matthew Pocernic, Brooke N Richtik, Patrick Clancy, Jacob Ruff, Mathew C Pula, James W Beare, Jonah Gautreau, Qiang Chen, Christopher R Wiebe, Graeme M Luke A breathing pyrochlore is a promising system to study magnetic frustration. It carries magnetic ions on the alternating array of corner-sharing small and large tetrahedra. This unique combination of bond alternation and magnetic frustration allows it to host various exotic phases. The breathing pyrochlore system is also predicted to host various types of quantum spin liquid. We will present the synthesis, and magnetic and physical properties of new breathing pyrochlore CuAlCr4S8 with the help of synchrotron x-ray diffraction (XRD), magnetic susceptibility, specific heat, zero-field (ZF)/ longitudinal-field (LF) muon spin relaxation/rotation (muSR). We find that CuAlCr4S8 orders antiferromagnetically at 20 K at ambient pressure, with the ordering temperature increasing to 23 K under 600MPa hydrostatic pressure. CuAlCr4S8 possesses one of the highest bond alternations among the chromium-based breathing pyrochlores discovered so far. |
Monday, March 14, 2022 10:12AM - 10:24AM |
A51.00010: Pinch point features below the critical temperature in frustrated pyrochlore magnets Daniel Lozano-Gomez, Kristian T Chung, Mingyu Shi, Michel J P Gingras Pinch points, sharp anisotropic reciprocal space features appearing in neutron scattering cross sections, are indicative of disordered yet highly correlated spin liquid phases. Recent work has clarified that pyrochlore spin liquid phases can be understood by splitting the degrees of freedom into two separate components, dubbed rotational and irrotational. In particular, it is possible for the irrotational modes to order while the rotational modes fluctuate as a spin liquid, yielding coexistence of Bragg peaks and pinch points in the neutron scattering cross section, a phenomenon dubbed "fragmentation". Inspired by this phenomenon, we show that spin wave fluctuations about ordered configurations can be characterized as "rotational-like" and "irrotational-like" in a number of pyrochlore spin models. We demonstrate how the contributions of these two components can be exposed in neutron scattering measurements and how they combine to produce pinch-point-like features in ordered and non-spin-liquid phases. Our work further clarifies the nature of pinch points and extends the notion of fragmentation as a ubiquitous principle in pyrochlore magnetism. |
Monday, March 14, 2022 10:24AM - 10:36AM |
A51.00011: The Quantum pyrochlore $S=\frac{1}{2}$ Heisenberg antiferromagnet at finite and zero temperature Robin Schaefer, Imre Hagymási, David Luitz, Roderich Moessner We use cutting-edge computational methods to investigate the pyrochlore $S=1/2$ antiferromagnet at finite and zero temperature. |
Monday, March 14, 2022 10:36AM - 10:48AM |
A51.00012: Sr3LiIrO6: a potential quantum spin liquid candidate in the one dimensional d4 iridate family Abhisek Bandyopadhyay, Sugata Ray Spin-orbit coupling (SOC) offers a large variety of novel and extraordinary magnetic and electronic properties in otherwise 'ordinary pool' of heavy ion oxides. Here we present a detailed study on an apparently isolated hexagonal 2H spin-chain d4 iridate Sr3LiIrO6 (SLIO). Our structural studies clearly reveal perfect Li-Ir chemical order in this compound. Our combined experimental and ab-initio electronic structure investigations establish a magnetic ground state with finite Ir5+ magnetic moments in this compound, contrary to the anticipated nonmagnetic J=0 state. Furthermore, the dc magnetic susceptibility, 7Li nuclear magnetic resonance, heat capacity and spin-polarized density functional theory studies unravel that despite having noticeable antiferromagnetic correlation among the Ir5+ local moments, this SLIO system evades any kind of magnetic ordering down to at least 2 K due to geometrical frustration, arising from the comparable interchain Ir-O-O-Ir superexchange interaction strengths, hence promoting SLIO as a potential quantum spin liquid candidate. Finally, the linear temperature dependence of the magnetic specific heat at low temperatures in both zero and applied magnetic fields suggest a gapless spinon density of states in this potential QSL candidate Sr3LiIrO6. |
Monday, March 14, 2022 10:48AM - 11:00AM |
A51.00013: Magnetic-Field-Dependent Thermodynamic Properties of Square and Quadrupolar Artificial Spin Ice Mateusz M Goryca, Xiaoyu Zhang, Justin D Watts, Cristiano Nisoli, Chris Leighton, Peter E Schiffer, Scott A Crooker Applied magnetic fields are an important tuning parameter for artificial spin ice (ASI) systems, as they can drive phase transitions between different magnetic ground states, or tune through regimes with high populations of emergent magnetic excitations (e.g., monopole-like quasiparticles). In this work, using both simulations and experiments, we thoroughly investigate the thermodynamic properties and magnetic phases of square and quadrupolar ASI as a function of applied in-plane magnetic fields. Monte Carlo (MC) simulations are used to generate field-dependent maps of the magnetization, the magnetic specific heat, and the thermodynamic magnetization fluctuations, all under equilibrium conditions. These maps reveal the diversity of magnetic orderings and the phase transitions that occur in different regions of the phase diagrams of these ASIs. Furthermore, the MC calculations allow us to probe the stability of different phases as a function of applied field and temperature. Those calculations are experimentally supported by magneto-optical measurements of the equilibrium "magnetization noise" in thermally-active ASIs. Our results provide a window into a rich landscape of collective magnetic behavior associated with the application of magnetic field to ASI systems. |
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