Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session T54: Skyrmions in Antiferromagnetic SystemsFocus Recordings Available
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Sponsoring Units: GMAG Chair: Jay Gupta, Ohio State University Room: McCormick Place W-476 |
Thursday, March 17, 2022 11:30AM - 11:42AM |
T54.00001: Micromagnetic modeling of spin dynamics in antiferromagnets and ferrimagnets Denis Pelekhov, Jacob B Freyermuth, Mohit Randeria Topological magnetic structures, such as skyrmions and domain walls, present great potential for technological applications in magnetic devices. We report on our progress in micromagnetic modeling of domain wall and skyrmion motion driven by electric currents, including spin transfer torque and/or spin orbit torque from the spin Hall effect, in antiferromagnetic and ferrimagnetic systems. We use a custom developed micromagnetic software package capable of modeling such systems, as well as ferromagnets. We investigate the influence of material parameters and methods of manipulation on domain wall and skyrmion velocities. |
Thursday, March 17, 2022 11:42AM - 11:54AM |
T54.00002: Atomistic Simulations of Antiferromagnetic Skyrmions' High-Speed Dynamics and Contrast with Domain Wall Motion Elizaveta Tremsina, Geoffrey S Beach High-velocity dynamics of Antiferromagnetic skyrmions (AFMSks), as well as their ability to display relativistic behavior, have yet to be fully understood. Unlike Domain Walls (DWs), their one-dimensional counterparts, AFMSks should not obey Lorentz invariance, because they have been claimed to be non-commutative solitons. It was also previously shown that AFMSks have a special critical velocity limit vc, always less than the magnon group speed, as dictated by the Dzyaloshinskii–Moriya interaction (DMI) which also serves to stabilize them in the material. Using VAMPIRE atomistic simulations, we show that AFMSks possess fundamentally different dynamic properties than DWs. We perform a systematic study of the dynamic deformations in skyrmion radius, as well as the width of their bounding domain wall, which we claim are universally related to the AFMSk velocity relative to the critical limit vc. We present a novel outlook on the role of skyrmion compactness in their deformation patterns, velocity limits, as well as the emergence or absence of behaviors similar to ones observed in relativistic DWs. These results could prove to be significant to the field of solitonics and the potential applications of AFMSks for novel logic and memory devices. |
Thursday, March 17, 2022 11:54AM - 12:06PM |
T54.00003: Noether spin current in noncollinear kagome antiferromagnet models Hua Chen, Luke Wernert Noncollinear antiferromagnets (AFMs) Mn3X (X=Ir, Sn, Ge, etc.) have recently attracted attention in the emerging field of antiferromagnetic spintronics because of their various interesting transport, magnetic, and optical properties. Due to the noncollinear magnetic order, spin is in general not a conserved quantity even without explicitly considering spin-orbit coupling, making it difficult to understand the transfer of angular momentum among different subsystems. Here we study the conserved Noether current and charge associated with spin rotation symmetry in noncollinear AFMs by considering a two-dimensional kagome lattice model with classical spins forming different noncollinear orders. Explicit formulas of the Noether spin current and charge were derived based on the continuum Lagrangian obtained through gradient expansion of the lattice model. We found that the Noether spin current of noncollinear AFMs carries information of the underlying lattice and ground state, and is inherently anisotropic even when the spin rotation symmetry is intact. We show the consequences of this unusual anisotropy by numerically studying evolutions of magnon wave packets scattered by magnetic domain walls. |
Thursday, March 17, 2022 12:06PM - 12:18PM |
T54.00004: Tunnel Magnetoresistance Detection of Skyrmions Hao Chen, Sara Majetich, William Bouckaert Skyrmions have been proposed for racetrack memory, but there are still many questions about the best way to detect them electronically. Mumax3 micromagnetic simulations were used to determine the core direction and chirality of skyrmions. A spin polarized current was used to move a Néel skyrmion down a racetrack that contains a circular magnetic dot above it to detect the core direction by tunnel magnetoresistance (TMR). When the skyrmion core and dot magnetizations are parallel, the skyrmion diameter grows slightly as it approaches the dot, since the dipolar field tends to orient misaligned spins. The spatial field gradient due to the dot causes a repulsive deflection around the dot and there is a transient drop in resistance. When the skyrmion core and dot magnetization are antiparallel, the skyrmion slightly shrinks in diameter as it approaches the dot, and there is an attractive interaction. The time profile then shows a transient. The chirality of a skyrmion is detected by an in-plane magnetized synthetic antiferromagnet detector, which creates smaller stray field compared to a single layered dot. A peak-dip or dip-peak feature in the time profile represents the chirality of the detected skyrmion. |
Thursday, March 17, 2022 12:18PM - 12:30PM |
T54.00005: On the Clock Frequency of the Néel-Vector Mode in Antiferromagnets Ralph Skomski, Ahsan Ullah, Balamurugan Balasubramanian, Christian Binek The potential use of antiferromagnets in high-frequency information processing is investigated by comparing different types of of Néel-vector rotations. The modes involve a competition between interatomic exchange J and anisotropy K, with basic frequencies in the ranges of several GHz (K) and several THz (J). Pure Néel-vector rotation (the propeller mode) yields GHz frequencies, whereas the scissor mode is exclusively based on J. The textbook analysis of antiferromagnetic resonance reveals a hybridization of propeller and scissor modes with precession frequencies scaling as (J K)1/2. In general, higher frequencies correspond to weaker signals, which is a challenge in AFM spintronics. Our focus is on multiferroic switching [1] using crystal-field interactions [2-3]. Using model calculations, we show that electrostatic crystal-field changes can lead to resonance with very large precession angles and eventually yields a propeller state that corresponds to a partial magnetization switching. |
Thursday, March 17, 2022 12:30PM - 12:42PM |
T54.00006: Self-hybridization of magnons in synthetic antiferromagnetic multilayers Mitra M Subedi, Yuzan Xiong, Peter B Meisenheimer, John T Heron, Wei Zhang, Joseph N Sklenar Antiferromagnets possess many potential applications due to their high-frequency dynamic properties. Here, we study combinations of ferromagnetic layers separated by non-magnetic layers of suitable thicknesses. These structures have an antiferromagnetic coupling between adjacent ferromagnetic layers and are called synthetic antiferromagnets. Synthetic antiferromagnets are useful materials for tuning magnon frequencies by manipulating magnon-magnon interactions. In this work, we consider Permalloy-Ru tetralayer structures. We previously predicted that tetralayers contain self-hybridization effect amongst acoustic or optical magnon pairs. We have now experimentally observed self-hybridization effects that are in close agreement with both macrospin model calculations and micromagnetic simulations. This work paves the way for electric tunability of magnon-magnon interactions. |
Thursday, March 17, 2022 12:42PM - 12:54PM |
T54.00007: Dzyaloshinskii-Moriya Interaction Enhanced Spin Pumping of an Easy-Plane Antiferromagnet Hailong Wang, Yuxuan Xiao, Mingda Guo, Eric Lee-Wong, Gerald Q Yan, Ran Cheng, Chunhui R Du Over the past decade, antiferromagnets have received immense interest due to their significant potential for developing ultrafast magnetic information storage. α-Fe2O3 is naturally relevant in this context due to its tunable magnetic structure and reduced resonance frequency. Here, we report dc spin pumping by the acoustic resonant mode in the canted easy-plane antiferromagnetic phase of α-Fe2O3 enabled by the Dzyaloshinskii-Moriya interaction. Systematic angle and frequency dependent measurements demonstrate that the observed spin pumping signals arise from resonance-induced spin injection and inverse spin Hall effect in α-Fe2O3/metal-based heterostructures, mimicking the behavior of spin pumping in conventional ferromagnet/nonmagnet systems. The pure spin current nature is further corroborated by reversal of the polarity of measured spin pumping signals when the metal layer is switched from platinum to tungsten which has an opposite sign of the spin Hall angle. Our results reveal the intriguing physics underlying the spin dynamics in canted easy-plane antiferromagnets-based heterostructures. |
Thursday, March 17, 2022 12:54PM - 1:06PM |
T54.00008: All-optical generation of antiferromagnetic magnon currents via the magnon circular photogalvanic effect Emil Vinas Boström The creation and control of spin currents at the nanoscale are key goals in spintronics and magnonics. One of the most promising approaches is to use optical means for spin current generation and control. Importantly, this would allow one to adapt concepts from photocurrent generation in electronic systems, in particular the circular photogalvanic effect. The CPGE holds great promise for functionality and applications since it allows to selectively generate currents and probe wavefunction quantum geometry only on the surface. We here introduce the magnon circular photogalvanic effect (MCPGE) as enabled by two-magnon Raman scattering. We show that a circularly polarized laser drive generates a magnon current whose strength and direction are controllable through the angle of incidence and polarization via the MCPGE. This magnonic photocurrent is predicted to lead to an inverse spin Hall voltage of experimentally accessible values in platinum contacts, with a characteristic angle dependence, enabling the experimental verification of both the magnon current generation and the underlying MCPGE with existing technology. The MCPGE as proposed in this work is the leading contribution to magnon photocurrents in antiferromagnetic insulators. |
Thursday, March 17, 2022 1:06PM - 1:18PM |
T54.00009: Engineering antiferromagnetic skyrmions and antiskyrmions at metallic interfaces Arnob Mukherjee, Deepak S Kathyat, Sanjeev Kumar We identify a mechanism to convert skyrmions and antiskyrmions into their antiferromagnetic (AFM) counterparts via interfacial engineering. The key idea is to combine the properties of an antiferromagnet and a spin-orbit (SO) coupled metal. Utilizing hybrid Monte Carlo (HMC) simulations for a generic microscopic electronic Hamiltonian for the interfacial layers, we explicitly show the emergence of AFM skyrmions and AFM antiskyrmions. We further show that an effective spin Hamiltonian provides a simpler understanding of the results. We discuss the role of electronic itinerancy in determining the nature of magnetic textures and demonstrate that the mechanism also allows for tuning of antiskyrmion size without changing the SO coupling. |
Thursday, March 17, 2022 1:18PM - 1:30PM |
T54.00010: Chirality readout of antiferromagnetic topological spin textures via quantum magnetometry Michael Hoegen, Mete Atature, Hariom K Jani, Paolo Radaelli, Anthony Tan, Helena Knowles, Matthew Feuer The recent discovery of ambient topological spin textures in the classical antiferromagnet (AF) α-Fe2O3 is a tremendous leap towards realizing AF spintronics. The presence of bulk Dzyaloshinskii-Moriya interaction in this AF system produces a small uncompensated magnetic moment generating weak stray fields (μT) which remains unexplored. In this study, we show for the first time the characteristic stray-field signature of various nanoscale AF topological quasiparticles with scanning NV magnetometry (SNVM). We evidence merons, antimerons and anti-phase domain walls above and below the Morin temperature (TM=200 K), and crucially demonstrate direct chirality readout. Remarkably, simulations and observed field signatures also suggest a magnetic charge imprint on topological AF quasiparticles. The table-top nanoscale imaging of two-dimension AF quasiparticles underlines the increasingly vital role of SNVM in accelerating research in the AF spintronics. |
Thursday, March 17, 2022 1:30PM - 1:42PM |
T54.00011: Skyrmions in synthetic antiferromagnets and their nucleation using electrical current and ultrafast laser illumination Olivier Boulle, Roméo Juge, Naveen Sisodia, Joseba Urrestarazu Larrañaga, Belkhou Rachid, Nina Novakovic-marinkovic, Mohamad-Assaad Mawass, Florian Kronast, Markus Weigand, Jörg Raabe, Lucia Aballe, Laurent Ranno Magnetic skyrmions are topological spin textures which hold great promise as nanometer scale information carriers in memory and logic devices. While room temperature magnetic skyrmions and their current induced manipulation were recently demonstrated [1–5], the stray field resulting from their magnetic moment as well as their topological charge limit their minimal size and reliable motion in tracks. Antiferromagnetic (AF) skyrmions allow to lift these limitations owing to their vanishing magnetic moment and canceled topological charge, promising room temperature ultrasmall skyrmions, fast dynamics and insensitivity to external magnetic fields. While room temperature AF spin textures have been recently demonstrated [6–9], the observation and controlled nucleation of AF skyrmions operable at room temperature in industry compatible AF material systems is still lacking. Here we demonstrate that isolated skyrmions can be stabilized at zero field and room temperature in a fully compensated SAF. SAF based on (Pt/Co/Ru/Pt/Co/NiFe) multilayers with vanishing magnetization were grown using magnetron sputtering. Using X-ray microscopy XMCD-PEEM and STXM, we observe chiral Néel domain walls as well as SAF skyrmions at zero external field and room temperature, with average diameters of 200 nm. By employing the corresponding X-ray energy, we are able to resolve the skyrmions in the different SAF layers and demonstrate their AF alignment. Magnetic microscopy , micromagnetic simulations and an analytical model confirm the SAF skyrmion homochirality and allow the identification of the physical parameters controlling their size and stability. We also show that the SAF skyrmions can be nucleated at zero magnetic field using local current injection as well as ultrafast laser excitations. These results pave the way for the use of SAF skyrmions in skyrmion based devices. |
Thursday, March 17, 2022 1:42PM - 2:18PM |
T54.00012: Antiferromagnetic Skyrmionics: generating and controlling topological textures Invited Speaker: Hariom K Jani Whirling magnetic textures could emerge as topologically protected information bits for next-generation computing. However, their practical adoption has been inhibited by susceptibility to stray fields, internal dipole fields, slow speed or sideway motion. To alleviate these issues, there has been a surge of interest in antiferromagnetic (AFM) analogues, predicted to be robust, scalable and ultra-fast. Yet, experimental progress in this field has been inhibited by the difficulty to visualize and control AFM textures via standard techniques. |
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