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 M55: Dynamics of Topological Spin TexturesFocus
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Sponsoring Units: GMAG Chair: Timothy Charlton, Oak Ridge National Lab Room: Room 305 |
Wednesday, March 8, 2023 8:00AM - 8:36AM |
M55.00001: Three-dimensional topological spin textures and their emergent electromagnetic dynamics Invited Speaker: Yizhou Liu Topological spin textures (TSTs) like magnetic skyrmions host intriguing physical properties and are promising candidates for next-general spintronic applications. TSTs in one- and two-dimensions have been extensively investigated. Recently, the interest in studying three-dimensional (3D) TSTs emerges as the addition of a spatial dimension endows spin textures with diverse structures and rich physics therein. Here, I will first discuss the realization of several 3D TSTs including chiral bobber lattice, skyrmionic vortex, and magnetic hopfion via engineering magnetic interactions in chiral magnets. These 3D TSTs give rise to emergent magnetic fields with sophisticated structures in which emergent magneto-multipoles can be further identified. I will show that the emergent magneto-multipoles characterize the nonlinear responses of TSTs. As an example, the nonlinear spin dynamics and electrical transports related to a hopfion will be discussed. |
Wednesday, March 8, 2023 8:36AM - 8:48AM |
M55.00002: Generation energetics of skyrmion bubbles concerning perpendicular magnetic anisotropy Albert M Park, Seungmo Yang, Moojune Song, Mujin You, Tae-Seong Ju, Chanyong Hwang, Kab-Jin Kim Skyrmion bubbles with non-trivial topological number emerge from a complex energy landscape that involves multiple magnetic energy contributions. While they hold a unique position in applications such as racetracks or logic devices due to their stability and controllability, the fundamental properties of their dynamics also gained considerable attention as they inevitably affect the operation of skyrmion devices. Especially the generation process of the skyrmions is known to depend critically on magnetic parameters [1], and the role of entropic effects on activation energy can vary widely depending on the detailed structure of the magnetic textures [2,3]. |
Wednesday, March 8, 2023 8:48AM - 9:00AM |
M55.00003: Peak Effect and Order to Disorder Transitions in Skyrmion Lattices Charles M Reichhardt, Cynthia Reichhardt The peak effect is a feature found in superconducting vortex systems with quenched disorder where, due to a softening of the vortex lattice due either to thermal effects or increasing magnetic field, there can be a strong enhancement of the critical depinning force [1,2]. An interesting feature of the peak effect is that in some cases, the critical depinning force can increase with increasing temperature, whereas in most systems an increase of thermal fluctuations leads to increased creep and a reduced depinning force. Here, using a recently proposed model where skyrmion-skyrmion interactions exponentially decrease with increasing temperature [3,4], we show that the skyrmion lattice also exhibits what we call a skyrmion peak effect. In this case, when the skyrmion-skyrmion interactions became weak enough, there is a transition from a skyrmion lattice to a glassy state that is much better pinned by the substrate. At even higher temperatures, there is an increase in the amount of thermal creep that causes the critical depinning force to decrease. This leads to a peak effect in the critical current, crossing effects in the velocity-force curves, and changes in the differential conductivity. We explore how the skyrmion Hall angle changes across this transition and map out the the general field versus temperature phase diagram showing skyrmion crystal, glass, and fluid regimes for varied values of quenched disorder. |
Wednesday, March 8, 2023 9:00AM - 9:12AM |
M55.00004: Anisotropic skyrmion mass induced by conduction electrons: a Schwinger-Keldysh functional integral approach Felipe Reyes Osorio, Branislav K Nikolic The current-driven motion of skyrmions in magnetic materials, as topologically protected winding vector fields of local magnetization, has attracted considerable attention due to both fundamental interest in dynamics of topological solitons and potential spintronic applications. While long-established Thiele equations capture its rigid motion [1] under the assumption of preserved skyrmion shape, experiments on realistic skyrmions [2] find deviation due to inertial mass which has been explained theoretically as the consequence of their internal dynamics [1, 3], geometry of the nanowire [4], and interactions with magnons [5] or phonons [6]. However, experimentally observed skyrmion mass is often much much larger than predicted by existing theories. In this study, we employ Schwinger-Keldysh functional integral approach to study electrons interacting with localized magnetic moments to obtain a stochastic equation of motion for skyrmions whose time-retarded damping kernel contains new anisotropic mass term generated by conduction electrons. |
Wednesday, March 8, 2023 9:12AM - 9:24AM |
M55.00005: Magnon dynamics in a Skyrmion-textured domain wall of antiferromagnets Seungho Lee, Kouki Nakata, Oleg Tchernyshyov, Se Kwon Kim We theoretically investigate the interaction between magnons and a Skyrmion-textured domain wall in a two-dimensional antiferromagnet and elucidate the resultant properties of magnon transport. Using supersymmetric quantum mechanics, we solve the scattering problem of magnons on top of the domain wall and obtain the exact solutions of propagating and bound magnon modes. Then, we find their properties of reflection and refraction in the Skyrmion-textured domain wall, where magnons experience an emergent magnetic field due to its non-trivial spin texture-induced effective gauge field. Based on the obtained scattering properties of magnons and the domain wall, we show that the thermal transport decreases as the domain wall's chirality increases. Our results suggest that the thermal transport of an antiferromagnet is tunable by modulating the Skyrmion charge density of the domain wall, which might be useful for realizing electrically tunable spin caloritronic devices. |
Wednesday, March 8, 2023 9:24AM - 9:36AM |
M55.00006: Machine Learning Model for Dynamics of Itinerant Frustrated Magnets Sheng Zhang, Gia-Wei Chern Itinerant magnets exhibit complex magnetization textures due to the long-range electron-mediated spin-spin interactions, which depend intimately on the underlying electron Fermi surface. The resultant effective spin Hamiltonian is often highly frustrated, giving rise to non-coplanar spin structures that endow the electrons with a nontrivial Berry phase. Of particular interest is magnetic skyrmions that play a crucial role in the emerging field of spintronics. However, accurate large-scale Landau-Lifshitz-Gilbert (LLG) dynamics simulation of itinerant magnets is computationally highly demanding due to the electron degrees of freedom, which have to be integrated out on-the-fly at every time-step. Here we present a general and scalable machine learning (ML) model for efficient and accurate prediction of local electron-induced effective fields. To demonstrate our approach, we incorporate the ML model, which is trained from small-size exact solutions, into large-scale LLG simulations to systematically study the phase-ordering dynamics of skyrmion crystals in the well-known s-d model of itinerant magnets. Our work opens a new avenue for multi-scale dynamical modeling of metallic spin systems. |
Wednesday, March 8, 2023 9:36AM - 9:48AM |
M55.00007: Skyrmion Coupling Modulated by Spatially Varying Magnetic Anisotropy Dreycen Foiles, Axel Hoffmann
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Wednesday, March 8, 2023 9:48AM - 10:00AM |
M55.00008: Role of Local Gyrotropic Force in Antiferromagnetic Skyrmion Deformations Elizaveta Tremsina, Geoffrey S Beach Past numerical studies have reported that antiferromagnetic skyrmions (AFMSks) exhibit elliptical deformations while in motion, followed by a full breakdown at a critical limiting velocity. The skyrmion equilibrium structure, as well as the limiting velocity have been shown to depend on several material parameters, namely, Heisenberg exchange, magnetic anisotropy and Dzyaloshinskii–Moriya interaction (DMI). However, the deformation mechanism in AFMSks has not yet been understood. In this work, the dynamics of skyrmions in antiferromagnetic (AFM) materials are studied utilizing atomistic simulations performed in the VAMPIRE software. It is well known that the total Magnus force acting on a skyrmion in a fully compensated AFM is zero, thus, its center of mass is not deflected. Here, using numerical simulations over a large range of material parameters, we demonstrate that the distortions and critical behavior are due to a local imbalance of the gyrotropic force which emerges when the AFMSk is in motion. We propose that this differential force is balanced by the restoring force acting to maintain skyrmion energy. Our model is consistent with numerical simulation data and provides a qualitative physical explanation of the deformation mechanism. These results not only expand the understanding of fundamental properties of magnetic skyrmions, but are significant for the understanding of AFMSks and their subsequent use in the field of spintronics. |
Wednesday, March 8, 2023 10:00AM - 10:12AM |
M55.00009: Skyrmion v.s. antiskyrmion Hall angles and Hall viscosity Bom Soo Kim Hall viscosity has been much studied theoretically in quantum Hall systems. We demonstrated, using quantum field theory Ward identities, that this Hall viscosity is also a part of universal transport coefficients in skyrmion motion. Here we advertise that Hall viscosity has a better chance to be verified through the difference between the skyrmion and antiskyrmion Hall angles, which is about 10% according to the available experimental data sets. |
Wednesday, March 8, 2023 10:12AM - 10:24AM |
M55.00010: Skyrmion lattice formation and destruction mechanisms probed with SANS Namila C Liyanage, Nan Tang, Lizabeth J Quigley, Guo-Jiun Shu, Fang-Cheng Chou, Nicholas P Butch, Markus Bleuel, Julie A Borchers, Lisa M DeBeer-Schmitt, Dustin A Gilbert A magnetic Skyrmions is a local whirl of the spin configuration in a magnetic material. These topologically stabilized quasi-particles have interesting applications in spintronic devices [1] also, these structures cannot be continuously created or destroyed. |
Wednesday, March 8, 2023 10:24AM - 10:36AM |
M55.00011: Quantum Hall Ferromagnetism and Skyrmions in the Hubbard-Hofstadter Model Jixun K Ding, Wen O Wang, Ziyan Zhu, Edwin W Huang, Brian Moritz, Thomas Devereaux It has been suggested that quantum Hall ferromagnetism at odd integer Landau filling factors and associated skyrmion excitations arise in the fermionic Hubbard-Hofstadter model. But current evidence for the existence of skyrmions and their region of stability in phase space is not conclusive. In this work, we use determinant quantum Monta Carlo to study the spin and charge correlations of the Hubbard-Hofstadter model on a triangular lattice to demonstrate the existence of both quantum Hall ferromagnetism and nearby skyrmionic states. We consider the effect of changing the relative strengths of Coulomb repulsion, orbital coupling and Zeeman coupling. Our study is relevant for understanding the behavior of strongly correlated electrons under large magnetic fields, particularly in bilayer TMD Moiré materials. |
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