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 Q55: Skyrmions and Chiral Spin Textures in Bulk Materials IFocus
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Sponsoring Units: GMAG Chair: Avadh Saxena, Los Alamos National Laboratory Room: Room 305 |
Wednesday, March 8, 2023 3:00PM - 3:36PM |
Q55.00001: Competing Magnetic Interactions and fluctuation driven anomalous and topological Hall effects in the RMn6Sn6 class of centrosymmetric structures Invited Speaker: Nirmal J Ghimire RMn6Sn6 compounds, where R is a rare earth element, are a recent addition to 3D systems with a kagome net of magnetic elements, where the Mn atoms form the kagome net in the basal plane of a hexagonal lattice. More interestingly, these compounds form a wide variety of magnetic structures due to various competing energy scales, including the interlayer nearest and next-nearest exchange interactions that can be tuned with external perturbations, such as magnetic field or doping. In this talk I will discuss magnetic structures of two compounds, YMn6Sn6 and TbMn6Sn6. The former orders antiferromagnetically at 345 K and quickly transitions into an incommensurate spiral below 333 K. For a magnetic field applied in the ab-plane, a series of competing phases, namely, a distorted spiral (DS), transverse conical spiral (TCS) and fan-like (FL) phases are stabilized before polarizing into the forced ferromagnetic (FF) state. In this field orientation, this compound shows an enigmatic topological Hall effect (THE) near room temperature within the TCS phase, which we attribute to the scalar spin chirality generated by a novel fluctuations-driven mechanism. TbMn6Sn6 orders ferrimagnetically with ferromagnetic Mn spins arranged antiparallel to the Tb spins at about 423 K. This compound features a highly unusual magnetic reorientation transition about 100 K below the Curie point, whereby all spins in the system, remaining collinear, rotate by 90 degrees, and also shows an unusual temperature dependence of the anomalous Hall conductivity. Both these effects find quantitative explanation in the fact that Mn and Tb, by virtue of the Mermin-Wagner theorem, have very different spin dynamics, with Tb spins experiencing much more rapid fluctuations. |
Wednesday, March 8, 2023 3:36PM - 3:48PM |
Q55.00002: Engineering a Skyrmion Crystal in Ferromagnetic/Antiferromagnetic Bilayers Based on the Magnetic Frustration Mechanism Kazuki Okigami, Ryota Yambe, Satoru Hayami A magnetic skyrmion crystal (SkX), which is a topologically nontrivial swirling spin texture, has attracted attention as the origin of the emergent electromagnetic phenomena. One of the stabilization mechanisms of the SkX is the Dzyaloshinskii-Moriya (DM) interaction. Recently, other mechanisms to stabilize the SkX have been clarified, such as short-range competing exchange interactions [1] and effective long-range exchange interactions mediated by itinerant electrons [2]. These mechanisms without the DM interaction might give a keen insight to understand the origins of the SkXs discovered in centrosymmetric magnets, such as Gd2PdSi3 and GdRu2Si2 [3]. |
Wednesday, March 8, 2023 3:48PM - 4:00PM |
Q55.00003: Control of emergent inductance in the helimagnet YMn6Sn6 by Tb substitution Aki Kitaori, Jonathan S White, Naoya Kanazawa, Victor Ukleev, Deepak Singh, Yuki Furukawa, Taka-hisa Arima, Naoto Nagaosa, Yoshinori Tokura Ac-current-driven motions of spiral spin textures can give rise to emergent electric fields and provide functionality as an inductor (emergent inductor) [1-2]. YMn6Sn6 is a helimagnet that shows the emergent inductance even above room temperature.[3] To identify the optimized material conditions for the phenomenon, we have investigated the effect of partial substitution of Tb for Y on the emergent inductance. Small-angle neutron scattering and inductance measurements have revealed that the pinning effect induced by Tb doping selectively and largely suppresses a negative component of the emergent inductance. We also find that in addition to the spin helix, the collinear antiferromagnetic structure can host positive emergent inductance due to spin fluctuations. |
Wednesday, March 8, 2023 4:00PM - 4:12PM |
Q55.00004: Optically controlled spin scalar chirality in centrosymmetric magnetic metals Atsushi Ono, Yutaka Akagi Noncoplanar and noncollinear spin textures such as magnetic skyrmions have attracted attention because of their intriguing topological nature and transport/optical properties due to emergent gauge fields. Such spin textures are stabilized by the Dzyaloshinskii-Moriya interaction (DMI) in noncentrosymmetric magnets and by the geometrical frustration or Fermi-surface instability in centrosymmetric magnets. Recently, an optical pulse has been found to be promising for creating and controlling spin textures on ultrafast time scales, albeit mainly in noncentrosymmetric magnets. |
Wednesday, March 8, 2023 4:12PM - 4:24PM |
Q55.00005: Bulk properties of Ni-intercalated metallic triangular antiferromagnet Ni1/3NbS2 and Ni1/3TaS2 Yeochan An, Pyeongjae Park, Kaixuan Zhang, Hyeoncheol Kim, Maxim Avdeev, Jaewon Kim, Myung Joon Han, Han-Jin Noh, Je-Geun Park TM1/3MS2 (TM = 3d transition metal, M = Nb, Ta) has recently been gaining increasing attention due to its wide variety of fascinating magnetic structures and the chiral arrangement of intercalated TM atoms. Here, we report the bulk properties of Ni1/3NbS2 and Ni1/3TaS2 by magnetization, transport, heat capacity, powder neutron diffraction, and X-ray absorption spectroscopy, which has received little attention compared to other TM1/3MS2. In particular, our work has determined the magnetic structure of Ni1/3NbS2 and Ni1/3TaS2 by neutron diffraction. Ni1/3NbS2 undergoes a phase transition at 84 K and develops antiferromagnetic helical order with a very long period along the c-axis (33c). On the other hand, a simple A-type spin configuration was observed for Ni1/3TaS2 below 158 K, where the spins are aligned to the c-axis. These magnetic structures, combined with lattice chirality and metallicity, can lead to various intriguing transport properties, making Ni1/3TaS2 and Ni1/3NbS2 promising material candidates for future studies on antiferromagnetic spintronics. |
Wednesday, March 8, 2023 4:24PM - 4:36PM |
Q55.00006: Electronic Structures of Chiral Helimagnetic Intercalated Transition Metal Dichalcogenides Lilia Xie, Oscar Gonzalez, Kejun LI, Matteo Michiardi, Marta Zonno, Sergey Gorovikov, Sergey Zhdanovich, Shannon S Fender, Na Hyun Jo, Sae Hee Ryu, Samra Husremovic, Matthew Erodici, Cameron Mollazadeh, Christopher Jozwiak, Aaron Bostwick, Eli Rotenberg, Andrea Damascelli, Yuan Ping, Kwabena Bediako Materials hosting topologically protected spin textures are appealing candidates for spintronic applications. The chiral helimagnets Cr1/3NbS2 and Cr1/3TaS2 are two such materials. Herein, we present a comparative study of their electronic structures using angle-resolved photoemission spectroscopy (ARPES). We find more dispersive bands in the Ta analogue, consistent with density functional theory (DFT) band structure calculations. The implications for the magnetic exchange interactions in these materials and the relative energy scales of their magnetic phase diagrams are discussed. We also propose assignments for experimentally observed bands near the Fermi level to surface vs. bulk states and discuss this model in the context of the chemistry of these materials. |
Wednesday, March 8, 2023 4:36PM - 4:48PM |
Q55.00007: Quantum phase transition and magneto-transport properties in a chiral helimagnet FeGe under high pressure Yukako Fujishiro, Chieko Terakura, Atsushi Miyake, Masashi Tokunaga, Naoya Kanazawa, Naoki Ogawa, Katsuya Shimizu, Yoshinori Tokura B20-type FeGe with a chiral crystal structure has been intensively studied as a near-room temperature skyrmion/helical magnet while an isostructural FeSi has attracted great attention as a narrow gap semiconductor with strong electron correlation effect. In this study, we report high-pressure magneto-transport properties in FeGe measured by using diamond anvil cell. The expected metal-insulator transition was not observed up to 30 GPa although the effective lattice constant should have reached that of FeSi at ~25 GPa. In the meanwhile, the quantum phase transition upon the suppression of long-range magnetic order was identified around the critical pressure of ~19 GPa, showing a non-Fermi liquid behavior in the electrical resistivity. Furthermore, various types of negative/positive magnetoresistance were observed, which indicates the presence of complex magnetic and electronic states in the high-pressure regime above the quantum phase transition. The result of Hall resistivity measurement will also be discussed in light of the topological non-Fermi liquid state which has been reported in the pressurized MnSi. |
Wednesday, March 8, 2023 4:48PM - 5:00PM |
Q55.00008: New vortex phase in antiferromagnetic incommensurate magnet Ba2CuGe2O7 Michal P Dembski-Villalta, Markus Garst, Benjamin Wolba, Éric Ressouche, Alexandra A Turrini, Alexander Engelhardt, Sebastian Mühlbauer Ba2CuGe2O7 is a quasi-2D insulator characterised by a tetragonal, noncentrosymmetric space group (P-421m) with Dzyaloshinskii–Moriya interactions (DMI). Because of the DMI, at ground state below TN = 3.05 K, it exhibits an almost AF cycloidal spin structure with a pitch of 220 Å. The magnetic structures of Ba2CuGe2O7 for different temperature and magnetic field values have been the topic of numerous experiments [1] indicating a rich phase diagram with a multitude of incommensurate (IC) phases. Following a recent theoretical prediction, the existence of a vortex phase [2] with non-trivial topological properties in Ba2CuGe2O7 has been verified experimentally, by means of neutron scattering and bulk measurements of specific heat and AC susceptibility. Particularly, hints towards the presence of a vortex phase were found in the neutron scattering data. There significant measured intensity is seen in the region of interest, noticeably higher than in the paramagnetic phase. This intensity is evenly distributed among four IC satellites on a square plane in reciprocal space, even in the presence of a small in-plane magnetic field component. However, it remains unclear whether the observed phase is due to static long range order or is a fluctuating dynamic texture that is on the verge of ordering. |
Wednesday, March 8, 2023 5:00PM - 5:12PM |
Q55.00009: Noncoplanar Spin Textures in Cubic Double Perovskites Ba2YRuO6 and Ba2LuRuO6 Joseph Paddison, Jiaqiang Yan, Hao Zhang, Seunghwan Do, Shang Gao, Matthew B Stone, David A Dahlbom, Kipton M Barros, Cristian Batista, Andy Christianson Magnetic materials with noncoplanar magnetic structures can show unusual physical properties driven by nontrivial topology. Topologically-active states are often multi-q structures, which are challenging to stabilize in models and to identify in materials. In this talk, we use inelastic neutron-scattering data to show that the insulating double perovskites Ba2YRuO6 and Ba2LuRuO6 -- previously assumed to be collinear antiferromagnets -- actually host a noncoplanar triple-q structure on the face-centered cubic lattice. I discuss the magnetic interactions that may stabilize this state, considering biquadratic exchange and cubic anisotropy. Our work identifies cubic double perovskites as a promising class of materials to realize topological magnetic states, elucidates the likely stabilization mechanism of the triple-q state in these materials, and establishes neutron spectroscopy on powder samples as a valuable technique to distinguish multi-q from single-q structures, facilitating the discovery of topologically-nontrivial magnetic materials. |
Wednesday, March 8, 2023 5:12PM - 5:24PM |
Q55.00010: Theory of Topological Electric and Thermoelectric Transport in Skyrmion Materials I Zachariah M Addison, Nishchhal Verma, Lauren Keyes, Mohit Randeria The Hall resistivity of chiral magnets is commonly analyzed as the sum of three terms: an anomalous Hall effect arising from spin-orbit coupling, a topological Hall signal deriving from a nonzero skyrmion density, and an ordinary Hall effect proportional to the external magnetic field. The theoretical justification for such a decomposition has long remained an open problem. Using a controlled semiclassical approach that includes all phase-space Berry curvatures [1], we show that the solution of the Boltzmann equation leads to a Hall resistivity that is just the sum of an intrinsic anomalous term arising from momentum-space curvature and a topological term related to the real-space curvature, in addition to the ordinary Hall effect. We generalize these results to calculate thermoelectric transport coefficients in chiral magnets in the next presentation. [1] N. Verma, Z. Addison, M. Randeria, arXiv:2203.07356 (2022) to appear in Science Adv.
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Wednesday, March 8, 2023 5:24PM - 5:36PM |
Q55.00011: Theory of Topological Electric and Thermoelectric Transport in Skyrmion Materials II Lauren Keyes, Zachariah M Addison, Nishchhal Verma, Mohit Randeria We analyze transport arising from electric field and thermal gradient induced perturbations to the distribution function in the presence of topological spin textures [1]. We include the effect of the anomalous velocity and eliminate that of the thermodynamic magnetization not measured in transport [2]. We derive a generalized Mott relation between the thermoelectric response and charge conductivity and find analytic expressions for the Seebeck and Nernst coefficients. We demonstrate these results for spin-orbit coupled conduction electrons in the presence of skyrmions and highlight interesting features that depend on the topology of the band structure. |
Wednesday, March 8, 2023 5:36PM - 5:48PM |
Q55.00012: Spectroscopic evidence for an antisymmetric Dzyaloshinskii-Moriya interaction in natural mineral brochantite Cu4SO4(OH)6 Andrey Podlesnyak, Tao Xie, S E Nikitin, A Gazizulilna, O Prokhnenko, L M Anovitz We report the direct observation of a commensurate-ordered antiferromagnetic (AFM) state but incommensurate helical spin dynamics in the natural mineral brochantite Cu4SO4(OH)6 through neutron diffraction and neutron spectroscopy in a magnetic field. We experimentally observe the effect of the Dzyaloshinskii-Moriya (DM) interaction, which elevates the degeneracy of the spin-wave modes shifting them in opposite directions in reciprocal space. We demonstrate that the system has a commensurate AFM ground state, stabilized by the anisotropic symmetric Heisenberg exchange interactions, and quasi-one-dimensional chiral spin dynamics due to the antisymmetric DM interaction. Employing linear spin-wave theory and density-matrix renormalization group calculations, we obtain both the symmetric exchange parameters and the DM vector components from the experimentally measured spin-wave spectra across the entire Brillouin zone. Our work provides detailed insights into the complex dynamics of the spin chain in the presence of DM interaction. |
Wednesday, March 8, 2023 5:48PM - 6:00PM |
Q55.00013: Manipulating chiral-spin transport in a room-temperature multiferroic Xianzhe Chen A collective excitation of the spin structure in a magnetic insulator can transmit spin-angular momentum with negligible dissipation. Here, we report the experimental observation of chiral-spin transport in multiferroic BiFeO3, where the spin transport is controlled by reversing the ferroelectric polarization and resultant chirality. The ferroelectrically controlled chiral magnons produce an unprecedented ratio of up to 40% rectification at room temperature. Utilizing these controllable chiral magnons in BiFeO3, an all-oxide, energy-scalable logic is demonstrated composed of spin-orbit injection, detection, and magnetoelectric control. This observation opens a new chapter of multiferroic magnons. |
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