Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session Q56: Cooperative Phenomena (Spin Structures, Spin Waves, Phase Transitions) I |
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Sponsoring Units: GMAG Chair: Junjie Yang, New Jersey Institute of Technology Room: Room 304 |
Wednesday, March 8, 2023 3:00PM - 3:12PM |
Q56.00001: Magnetic states in the itinerant magnets Vladimir P Antropov A new classification of magnetic materials using their degree of itinerancy is proposed. The classification produced a variety of magnetic states near the magnetic instability point. Several types of itinerant magnets are determined and their corresponding analogs among known systems are identified. We discuss the degree of the short-range magnetic order in such systems and establish a criterion for its appearance. The appearance of a smooth transition from the localized (Heisenberg) magnets to the itinerant (Stoner) ones is demonstrated for the intermediate type of magnets. Realistic calculations of magnetic states developing at finite temperatures in several typical ferro- and antiferromagnetic itinerant systems (Ni, Co, Cr, and so on) confirm the results of the proposed model and demonstrate new and unusual transformations of magnetic behavior in such systems. |
Wednesday, March 8, 2023 3:12PM - 3:24PM |
Q56.00002: Bimodal approach to investigating fluctuations in van der Waals antiferromagnets Calvin C Bales, Kemp Plumb, Alexander Zaslavsky, John B Marston, Gang Xiao, Vesna F Mitrovic Multimodal spectroscopy can be used to provide a more complete picture of the nature of fluctuations in van der Waals antiferromagnets approaching a two-dimensional antiferromagnetic transition. Nuclear magnetic resonance (NMR) and sensors based on magnetic tunneling junctions (MTJs) are used to provide complementary information about the nature of these fluctuations. NMR is a good probe of fluctuations within the entire material whereas MTJs can detect magnetic fluctuations with high spatial and temporal resolution. In this way, these two methods of spectroscopy complement each other by providing insights into the fluctuations within the sample as a whole and at a more localized level. This talk will discuss the results of measuring van der Waals antiferromagnets using this bimodal approach. |
Wednesday, March 8, 2023 3:24PM - 3:36PM |
Q56.00003: A Scanning Fabry Perot Cavity for the Investigation of THz Frequency Magnon Polaritons Jacob A Burgess, Aimé Braconnier, Akif Ahmed, Josh Gibbs, Christina Balanduk, Sangeev Selvaratnam, Can-Ming Hu The formation of hybrid quasiparticles in strongly interacting light-matter systems is of increasing interest due to the potential applications as sensors or in other devices. Here we present the a scanning Fabry-Perot cavity designed to be used with a time-domain THz spectrometer to investigate the formation of polaritons that form as a result of coupling between cavity photons and samples stored inside the cavity. The cavity makes use of custom fabricated silicon Bragg reflectors to achieve a balance between overall transmission and high quality factor for the cavity. We will present initial results of the instrument applied in a search for coupling between THz photons and magnons. |
Wednesday, March 8, 2023 3:36PM - 3:48PM |
Q56.00004: Observation of spin dynamics associated with exotic helical spin orders in EuIn2As2 Elizabeth Donoway, Alexander Liebman-pelaez, Joseph W Orenstein, Veronika Sunko, Ryan Day, Kohtaro Yamakawa, Yue Sun Layered antiferromagnetic materials provide a fertile playground for probing exotic magnetic orders, as well as for developing new approaches to manipulate magnetization dynamics for novel spintronic devices. In order to harness the excitations associated with these unconventional magnetic phases, it is crucial to characterize the largely unexplored collective spin modes that emerge within them. In this talk, I focus on our recent all-optical studies of time-resolved spin dynamics in the helical antiferromagnet EuIn2As2, wherein we detect magnons associated with distinct and broken helical spin phases for the first time. We demonstrate the evolution of these coherent magnon modes with magnetic field and temperature, illustrating their emergence with different magnetic orders, and use this to describe the magnetic phase diagram and dynamical spin landscape in EuIn2As2. |
Wednesday, March 8, 2023 3:48PM - 4:00PM |
Q56.00005: Low-temperature orthorhombic phase stabilization and magneto-dielectric coupling in Mn2.7Cr0.3O4 Hsiung Chou, Gopeshwar Dhar Dwivedi, S. M. Kumawat, C. W. Wang, D. Chandrasekhar Kakarla, H. D. Yang, S. J. Sun Spinel Mn2.7Cr0.3O4 exhibits ferrimagnetic transition and dielectric anomaly simultaneously around 45K. This suggests a correlation between magnetic and dielectric behaviors. A temperature-dependent neutron powder diffraction study revealed a simultaneous structural (tetragonal to orthorhombic phase) and magnetic transition in Mn2.7Cr0.3O4, i.e., the magnetic and structural transitions are linked. These results suggests the spin-lattice coupling controls magneto-dielectric behaviour of Mn2.7Cr0.3O4. The magnetic structure obtained from neutron diffraction study suggests that intrachain octahedral-octahedral exchange interaction is the most prominent interaction which provides canted antiferromagnetic (AFM) spin arrangement to the system. This results is contrary to the general belief that interaction between tetrahedral-octahedral cations are most prominent in the spinel systems. |
Wednesday, March 8, 2023 4:00PM - 4:12PM |
Q56.00006: Terahertz-frequency magnon upconversion unveiled by two-dimensional magnetic resonance spectroscopy Zhuquan Zhang, Frank Y Gao, Yu-Che Chen, Zi-Jie Liu, Jonathan B Curtis, Eric R Sung, Xiaoxuan Ma, Shixun Cao, Prineha Narang, Alex von Hoegen, Edoardo Baldini, Keith A Nelson The dynamic manipulation of nonlinear phonon-phonon interactions has arisen as a potent scheme to functionalize the properties of materials. Extensions of such a strategy to collective spin-waves could provide an attractive avenue for high-speed information processing based upon nonlinear coupled magnonics. Here, we discover that intense terahertz (THz) fields can initiate coherent magnon upconversion. By using a suite of single-shot multidimensional THz spectroscopy measurements on the canted antiferromagnet ErFeO3, we unveil the unidirectional nature of the coupling between distinct magnon modes. Analysis of the temperature-dependent spin dynamics demonstrates that this energy transfer originates from a complex interplay of competing nonlinear pathways. Our results demonstrate a route to inducing directional energy transfer phenomena between coherent magnons in magnetic materials and pave the way for a new generation of magnonic signal processing devices. |
Wednesday, March 8, 2023 4:12PM - 4:24PM |
Q56.00007: A Novel Route to Order-by-Disorder in a Ferromagnet Alexander Hickey, Daniel Lozano-Gomez, Vincent Noculak, Yasir Iqbal, Johannes Reuther, Michel J P Gingras Order-by-disorder, whereby fluctuations lift an accidental symmetry to stabilize a collection of broken symmetry states, is a recurrent and prominent theme in the field of frustrated magnetic systems with magnetic moments, or spins, subject to competing interactions. Thus far, such a phenomenon has been observed in systems where the selected state is not a true ground state of the quantum Hamiltonian. In part motivated by the ferromagnet pyrochlore oxides Lu2V2O7 and Y2V2O7, we present results exposing a novel route to order-by-disorder in a pyrochlore ferromagnet with spin-orbit interactions, where the selection is purely thermal, unaffected by zero-point fluctuations, and where the selected states are true ground states of the quantum Hamiltonian. We show that this selection can be explained solely from the thermal population of single-magnon bands. In certain circumstances, using both linear spin-wave theory and classical Monte Carlo simulations, one or more spontaneous rotations of the magnetization axis is found at intermediate temperature(s) within the ferromagnetic phase. |
Wednesday, March 8, 2023 4:24PM - 4:36PM |
Q56.00008: Evolution of electrodynamics upon thermal and photo-induced phase transitions in FeRh Kim Hyo Seok, Inhyeok Choi, Sungkyun Park, Chul kang, Hyeng Mun KIM, Min Seop KIM, Sehwan Song, Hee Jun Shin FeRh is an antiferromagnetic metal at room temperature, and undergoes magnetic and structural transitions around 370 K accompanied by a change in the electronic property. Photoexcitation also can drive similar changes in structural, magnetic, and electronic properties, and there have been extensive investigations to reveal whether the transitions of these properties occur simultaneously or not. In this work, we investigate evolutions of electrodynamics upon thermal and photo-induced phase transitions. We discuss in detail how electrodynamic properties are influenced by magnetic and structural changes |
Wednesday, March 8, 2023 4:36PM - 4:48PM |
Q56.00009: Systematic Derivation of Spin Hamiltonian with Higher-Order Terms by Spin S Representation Hiroshi Katsumoto, Stefan Blügel, Fabian R Lux, Yuriy Mokrousov It is known that complex magnetism emerge from competing Heisenberg interaction and higher-order spin interactions [1]. In addition, previously unknown interactions, such as the Chiral-Chiral interaction due to topological orbital magnetism, have been found to be essential in explaining magnetism [2]. It is beginning to be recognized that the higher order terms of such spin interactions depend not only on the number of sites of magnetic ions, but also on the local spin magnitude S. However, a method to uniquely derive a spin Hamiltonian that captures the spin interaction for a given system has not yet been established. In this presentation, we focus on the algebraic nature of the spin operator and give an exact spin Hamiltonian of the isotropic spin interaction for a given total local spin S and the number of magnetic sites. The derivation of the spin Hamiltonian is obtained from operators with the spin S representation depending on the spin magnitude. By organizing the algebraic structure followed by the general spin operators, we discuss the construction of the exact spin Hamiltonian, especially for S=1/2 and 1, including the higher-order terms of the interaction. Higher-order terms of scalar spin chirality obtained by this algebraic method will also be discussed. These results have applications not only to magnetism in solids, but also to nuclei or cold atom systems. |
Wednesday, March 8, 2023 4:48PM - 5:00PM |
Q56.00010: Crossover in the phase-coexistence between models with discrete and continuous variables Florian Kischel, Nils Caci, Stefan Wessel The relative weight of the distinct phases that coexist at a first-order phase transition in systems with discrete degrees of freedom is well understood. For example, in the q-state Potts model, it is characterized by a ratio R=1:q of the disordered vs. ordered regions. In models with continuous variables on the other hand, this ratio is generally unknown. Several recent instances however suggest that it equals R=1:IO, where IO denotes the integral measure of the space of extremal states of the ordered phase. In order to explore the emergence of this integral measure, we examine a system that realizes a crossover from discrete to continuous variables and study the behavior of R at its phase-coexistence points. In particular, we consider a generalized n-state clock-model on a three-dimensional simple cubic lattice with both bilinear and biquadratic exchange interactions. In the large-n (XY) limit, this model is known to harbor a first-order thermal phase transition, as does the 3-state Potts model, to which the model reduces in the limit of n=3. Here, we explore the phase-coexistence over the range of intermediate values of n using large-scale Monte Carlo simulations. |
Wednesday, March 8, 2023 5:00PM - 5:12PM |
Q56.00011: Strain induced magnetic phase behavior of a frustrated helimagnet Alexander Liebman-pelaez, Joseph W Orenstein, Elizabeth Donoway, Veronika Sunko Strain provides an exciting non-thermal parameter for exploring the rich phase diagrams of complex magnetic materials. Such systems are often characterized by a delicate balance between frustrated exchange interactions, magnetocrystalline anisotropy, and dipolar interactions, which can be strongly sensitive to uniaxial lattice distortions. Here we employ strain to traverse the phase diagram of EuIn2As2, a frustrated metallic helimagnet, under a magneto-optical probe. Our work demonstrates an efficient method of strain engineering magnetic materials and opens the door to tuning non-equilibrium magnetic phenomena such as spin transport. |
Wednesday, March 8, 2023 5:12PM - 5:24PM |
Q56.00012: Formation of a Simple Cubic Antiferromagnet Through Charge Ordering Vincent C Morano, Tanya Berry, Tom Halloran, Jason Zhang, Aashish Sapkota, Weiwei Xie, Zhijun Xu, Yang Zhao, Jeffrey W Lynn, Tom Fennell, Paul C Canfield, Tyrel M McQueen, Collin L Broholm EuPd3S4 is a mixed-valent lattice in which the BCC Eu2+ and Eu3+ ions occur in about a 1:1 ratio. The magnetic order below TN=2.9 K, however, has not been directly probed. Here we report what are to our knowledge the first neutron diffraction results on EuPd3S4 single-crystals, as well as comprehensive heat capacity measurements revealing the magnetic phase diagram. In addition to identifying k=(1/2,1/2,1/2) antiferromagnetic order, we find forbidden nuclear reflections in the field-polarized paramagnetic state. Our results resolve a longstanding question regarding charge ordering in EuPd3S4, showing the glide symmetries connecting Eu 2a sites are in-fact broken and the space group is of lower symmetry than previously understood. |
Wednesday, March 8, 2023 5:24PM - 5:36PM |
Q56.00013: A Multi-Modal Spectroscopy Technique to Probe Emergent Quantum Order using Magnetic Resonance Ilija K Nikolov, Rong Cong, Stephen Carr, Adrian G Del Maestro, Chandrasekhar Ramanathan, Vesna F Mitrovic The quadrupolar interaction between a nuclear spin and its local electric environment describes the local point-group symmetry and imprints information into the spin's dynamics. In traditional magnetic resonance, this information is encoded in the spectra. But it is easily obscured by multiple sources of spectral broadening, including non-trivial multipolar exchange interactions and zero local values of susceptibility. This is particularly relevant for materials that exhibit an emergence of exotic quantum phases that possess unusual symmetries and orderings, whose order parameters have large variations near phase transitions, and oftentimes zero mean. |
Wednesday, March 8, 2023 5:36PM - 5:48PM |
Q56.00014: Uniaxial ferromagnetism in the vanadium-based kagome metal TbV6Sn6 Ganesh Pokharel, Brenden Ortiz, Juan Chamorro, Paul M Sarte, Linus Kautzsch, Guang Wu, Stephen D Wilson Vanadium-based kagome metals RV6Sn6 (R=rare earth) are appealing candidates for exploring the interplay between R-site magnetism and nontrivial band topology associated with the nonmagnetic vanadium-based kagome network. Here we present the synthesis and characterization of TbV6Sn6 via single crystal X-ray diffraction, magnetization, transport, and heat capacity measurements. Magnetization measurements reveal strong, uniaxial magnetic anisotropy rooted in the alignment of Tb3+ moments in the interplane direction below 4.3(2) K. TbV6Sn6 exhibits multiband transport behavior with high mobilities of charge carriers, and our measurements suggest TbV6Sn6 is a promising candidate for hosting Chern gaps driven via the interplay between strong spin-orbit coupling, Tb-site magnetic order and the band topology of the V-site kagome network. |
Wednesday, March 8, 2023 5:48PM - 6:00PM |
Q56.00015: Evolution of magnetic properties along the LnCo2Al8 (Ln = La-Nd, Sm and Gd) intermetallic series of compounds RAQUEL A RIBEIRO, Cris Adriano, Sushma Kumari, Zhuoq Li, Aashish Sapkota, Juan Schmidt, Tyler J Slade, Sergey L Budko, Paul C Canfield The evolution of the magnetic properties along the series of intermetallic compounds LnCo2Al8 (Ln = La-Sm and Gd) is discussed and compared to earlier work [1]. Single crystals of the orthorhombic Pbam structures were grown out of excess Al-flux. Specific heat, anisotropic electrical resistivity, and magnetization measurements indicate that the Ln = Pr, Nd, Sm and Gd compounds order antiferromagnetically, presenting magnetic anisotropy with the easy axis along the crystallographic c-direction. Ln = Pr orders at TN = 4.9 K with a spin reorientation at 4.6 K while Ln = Nd orders at TN = 8.2 K with a spin reorientation at 2.7 K. Ln = Sm orders at TN = 21 K and Ln = Gd orders at TN = 8.4 K. For Ln = Ce we see signatures of a ferromagnetic-like transition near 5 K. Details of the evolution of metamagnetic transitions as well as possible Kondo-lattice behavior in CeCo2Al8 will be discussed. |
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