Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session E40: Skyrmions in Ferrimagnets and AntiferromagnetsFocus Live
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Sponsoring Units: GMAG DMP Chair: Flaviano dos Santos, Ecole Polytechnique Federale de Lausanne |
Tuesday, March 16, 2021 8:00AM - 8:36AM Live |
E40.00001: Manipulating Chiral Spin Textures in Compensated Ferrimagnets Invited Speaker: Lucas Caretta A promising approach to encode bits of information for next-generation memory and logic is by using solitons, such as domain walls (DW) or topological skyrmions, which can be translated by currents across racetrack-like wire devices. One technological and scientific challenge is to stabilize small spin textures and to move them efficiently with high velocities, which is critical for dense, fast memory and logic. However, in ferromagnetic materials, current-driven spin texture dynamics faced a “speed limit” of a few hundred m/s, and room-temperature-stable magnetic skyrmions were an order of magnitude too large to be useful in any competitive technologies. These problems were rooted in two fundamental characteristics of ferromagnets: large stray fields, which limit packing density, and precessional dynamics, which limit speed. By using a broader class of compensated metallic and insulating ferrimagnets, fundamental limits plaguing ferromagnets can be overcome. Here, we engineer chiral ferrimagnets with reduced magnetization (M) and angular momentum (S) to realize order of magnitude improvements in bit size and speed. In metallic, ferrimagnetic Pt/GdCo/TaOx films with sizeable Dzyaloshinskii–Moriya interaction, we realize current-driven DW motion of 1.3 km/s near the angular momentum compensation temperature and room-temperature-stable skyrmions with ~10 nm diameters near the magnetic compensation temperature. Moreover, by exploiting reduced S and low-dissipation in insulating garnets, we drive DWs to their relativistic limit using, achieving velocities in excess of 4300 m/s. We observe key signatures of relativistic motion including Lorentz contraction and velocity saturation. The experimental results are well-explained through analytical and atomistic modeling. These observations provide insight into the fundamental limits of magnetic soliton dynamics and establish a readily-accessible experimental framework to study relativistic solitonic physics. |
Tuesday, March 16, 2021 8:36AM - 8:48AM Live |
E40.00002: Current-induced spin-orbit torque switching of chiral magnetization across a synthetic antiferromagnet with built-in planar asymmetry Kang Wang, Lijuan Qian, Seechen Ying, Gang Xiao The interfacial Dzyaloshinskii-Moriya interaction (DMI) holds promises for design and control of chiral spin textures in low-dimensional magnets with efficient current-driven dynamics. In this talk, we discuss about the nature and control of chiral magnetization across a synthetic antiferromagnet (SAF) where an interlayer DMI is present between magnetic layers separated by a heavy-metal spacer. We first show the demonstration of the existence of interlayer DMI in our SAF with both inversion and in-plane asymmetry. We then show the study of current-induced spin-orbit torque (SOT) switching of magnetization in the SAF. The chiral nature of the interlayer DMI leads to an asymmetric SOT switching of magnetization under an in-plane magnetic field. According to our numerical studies, in the switching process, the effective field of the interlayer DMI switches its direction from antiparallel to parallel, or from parallel to antiparallel, to the direction of the damping-like field, respectively promoting or hindering the switching of magnetization. Finally, we will give an outlook of potential applications of our findings in future SOT and domain wall-based devices. |
Tuesday, March 16, 2021 8:48AM - 9:00AM Live |
E40.00003: Spin waves in an antiferromanget with a local triangular symmetry Sayak Dasgupta, Oleg Tchernyshyov We construct a field-theoretic description of spin waves in hexagonal antiferromagnets with three magnetic sublattices and coplanar 1200 magnetic order [1]. The three Goldstone modes can be separated by point-group symmetry into a singlet α0 and a doublet β. The α0 singlet is described by the standard theory of a free relativistic scalar field. The field theory of the β doublet is analogous to the theory of elasticity of a two-dimensional isotropic solid with distinct longitudinal and transverse “speeds of sound.” The speeds of sound can be readily calculated for any lattice model. We apply this approach to the compounds of the Mn3X family with stacked kagome layers and extract the exchange coefficients for a model spin Hamiltonian by fitting to neutron scattering data [2]. |
Tuesday, March 16, 2021 9:00AM - 9:12AM Live |
E40.00004: Interfacial Dzyaloshinskii-Moriya Interaction of Collinear Antiferromagnets MnPt and NiO on W, Re, and Au Md. Rakibul Karim Akanda, In Jun Park, Roger Lake The interfacial Dzyaloshinskii-Moriya interaction (iDMI), which is found at the interface between a magnetic material and a heavy metal (HM), favors noncollinear spin configurations. The iDMI values have been calculated for the antiferromagnetic (AFM) materials MnPt and NiO in proximity with the heavy metals W, Re, and Au as a function of the thicknesses of both the AFM layer and the HM layer. The iDMI values of the MnPt-W and MnPt-Re heterolayers are comparable to those of the common ferromagnetic materials, and those of NiO-Au are approximately 7 times lower. The saturation magnetization, exchange stiffness, and magnetic anisotropy constants are also calculated as functions of layer thicknesses. These values will provide required input parameters for micromagnetic modelling of antiferromagnetic skyrmions. |
Tuesday, March 16, 2021 9:12AM - 9:24AM Live |
E40.00005: Magnon-phonon hybridization in the quasi-2D antiferromagnet MnPSe3 Thuc Mai, Kevin Garrity, Amber McCreary, Nhan V Nguyen, Josh Argo, Jeffrey Simpson, Vicky Doan-Nguyen, Rolando Valdes Aguilar, Angela Hight Walker Magnetic excitations in van der Waals (vdW) materials, especially in the two-dimensional (2D) limit, is an interesting research topic from both the fundamental and application perspectives. In MnPSe3, a vdW material that could potentially host 2D antiferromagnetism (AFM), we identify the hybridization of two-magnon excitations with two separate Eg phonons using temperature-dependent magneto-Raman spectroscopy. We construct a model that reproduces our observations and demonstrates that the phonons and two-magnon excitations are hybridized in the magnetically ordered state. We also systematically study the overall Raman scattering intensity enhancement in the AFM phase. Our experimental and theoretical results points the the cause of spin-ordering-induced resonant Raman scattering effect in MnPSe3. |
Tuesday, March 16, 2021 9:24AM - 9:36AM Live |
E40.00006: Coupled Skyrmion Breathing Modes in Synthetic Ferri- and Antiferromagnets Martin Lonsky, Axel F Hoffmann Magnetic multilayers can combine strong spin-orbit interaction with lacking inversion symmetry, which may give rise to the presence of topologically nontrivial spin textures, so-called skyrmions. Recent studies have indicated enhanced propagation velocities of skyrmions in antiferromagnets and compensated ferrimagnets [1]. At the same time, it is unclear how magnetic compensation affects the dynamic excitations of magnetic skyrmions, such as breathing modes, which entail an oscillation of the skyrmion size at GHz frequencies [2]. Here, we present micromagnetic simulations of these resonance modes in synthetic ferri- and antiferromagnets. The observed features in the calculated power spectra are related to pure in-phase and anti-phase breathing modes as well as to hybridizations of breathing and spin wave modes that are characteristic for the considered circular-shaped geometry [3]. Based on these simulations, we then discuss the impact of these results for potential skyrmion sensing. |
Tuesday, March 16, 2021 9:36AM - 9:48AM Live |
E40.00007: Role of interlayer interactions in the recovery of synthetic ferrimagnetic skyrmions in [Co/Gd/Pt]n multilayers after cycling through the spin reorientation transition Alexandra R. Stuart, Xiao Wang, Adzo Fiagbenu, Kristen S. Buchanan, Xuemei Cheng Antiferromagnetic (AFM) skyrmions offer potential technological advantages for spintronic devices since the skyrmions are less prone to skyrmion Hall effects, and recent work also shows that large current-driven velocities are also possible. Here we use micromagnetic simulations to gain insight into a spin memory effect that was recently demonstrated experimentally for synthetic AFM skyrmion pairs in [Co/Gd/Pt]n=10 multilayered thin films. The synthetic AFM skyrmion pairs form in the Co due to the perpendicular anisotropy and interfacial Dzyaloshinkii Moriya interactions (DMI) that arise at the Co/Pt interface and are mirrored in the Gd due to the AFM exchange coupling between the Co and Gd layers. The skyrmions are erased when the temperature is lowered below the spin reorientation temperature and then recovered on rewarming. The simulations show that the DMIs play an essential role in the observed spin memory effect. We also explore the role of intralayer interactions on the spin memory process and show that although the stray fields from the other repeat units can influence the complexity of the low temperature in-plane distributions, the spin memory effect remains robust. |
Tuesday, March 16, 2021 9:48AM - 10:00AM Live |
E40.00008: Effects of geometry on curvilinear antiferromagnetic spin chains Oleksandr Pylypovskyi, Denys Y. Kononenko, Kostiantyn Yershov, Ulrich Roessler, Juergen Fassbender, Jeroen Van den Brink, Dennis Makarov, Denis D. Sheka Antiferromagnets are technologically promising materials for spintronic and spinorbirtonic devices [1]. An efficient manipulation of antiferromagnetic textures requires the presence of the Dzyaloshinskii-Moriya interaction (DMI), which is present in crystals of special symmetry, and thus limits the number of available materials. In contrast to antiferromagnets, it is already established that in ferromagnetic thin films and nanowires chiral responses can be tailored relying on curvilinear geometries [2]. Here, we explore geometry-induced effects in curvilinear antiferromagnets. We demonstrate theoretically that intrinsically achiral curvilinear antiferromagnetic spin chains behave as a biaxial chiral helimagnet with a curvature-tunable anisotropy and DMI [3]. The geometry-driven easy axis anisotropy determines the homogeneous antiferromagnetic state at low curvatures and the gap for spin waves. The geometry-driven DMI determines the helimagnetic phase transition and leads to the appearance of the region with the negative group velocity at the dispersion curve. |
Tuesday, March 16, 2021 10:00AM - 10:12AM Live |
E40.00009: Antiferromagnetic Skyrmions and Skyrmion Density Wave in Rashba Hund’s Insulator. Arnob Mukherjee, Deepak Kathyat, Sanjeev Kumar We discover magnetic phases hosting highly elusive and technologically important antiferromagnetic skyrmion quasiparticles in a model for Rashba-coupled Hund’s insulator. The results are based on unbiased simulations of a classical super-exchange model derived, in this work, from a realistic microscopic electronic Hamiltonian. We also discover a novel skyrmion density wave ground state characterized by a (Q, Q) modulation in the local skyrmion density map. A unique inhomogeneous state characterized by a circular pattern in spin structure factor and filamentary real-space textures is identified as the parent of sparse antiferromagnetic skyrmions. We predict that the magnetic states reported here can be realized in thin films of multiorbital systems involving 4d or 5d transition metals. |
Tuesday, March 16, 2021 10:12AM - 10:24AM Live |
E40.00010: Controlling long-range skyrmion lattices using field and temperature in Fe/Gd multilayers Lisa DeBeer-Schmitt, Ryan Desautels, Nan Tang, Sergio A Montoya, W.L.N.C Liyanage, Sheena Patel, Michael Fitzsimmons, Eric Fullerton, Julie Borchers, Dustin Gilbert To facilitate the realization of skyrmion-based devices, there is a need to design and develop materials that can host skyrmions under ambient conditions. We have fabricated thin-films of amorphous Fe/Gd multilayers that support skyrmions and skyrmion lattices at room temperature and zero applied magnetic field. By varying the film thickness and alloy composition, we can alter the balance of the dipole interactions relative to the exchange and anisotropy. Using small angle neutron scattering (SANS), we demonstrate a skyrmion lattice exists over a broad field and temperature range (including positive/negative/zero magnetic field and temperatures between 10K and 325 K, in a single film). By monitoring the temperature- and field-dependent scattering vector changes, we observe two skyrmion lattice spacing effects: increasing the field to positive saturation results in a decrease in Q suggesting an increase in the skyrmion lattice, while decreasing the field towards negative saturation results in an in Q before skyrmion lattice destabilizes. |
Tuesday, March 16, 2021 10:24AM - 10:36AM Live |
E40.00011: Spin texture dynamics in amorphous Fe-Ge films Xiaoqian Chen, Robert Streubel, Dinah Simone D Bouma, Roland Koch, Sophie A Morley, Stephen Douglas Kevan, Frances Hellman, Peter Fischer, Sujoy Roy Logic and memory devices created from novel spin-orbit materials are scalable and energy-efficient alternate to the current CMOS devices. Recent studies show that spin textures and Skyrmions that have been observed in well-known ferrimagnet FeGe can also form in pseudo-amorphous FexG1-x films (a-FeGe) due to a local DMI interaction. Yet, the exact magnetic field-temperature phase diagram and the nature of the magnetic transitions are yet to be understood. We used resonant coherent x-ray scattering and studied magnetic order parameters and spin texture dynamics across two magnetic phase transitions in a-FeGe. Characteristic curvatures from respective one-time correlation functions indicate the distinct dynamical behavior of the helical and skyrmion textures. |
Tuesday, March 16, 2021 10:36AM - 10:48AM Live |
E40.00012: Stabilization of zero-field skyrmions in synthetic antiferromagnetic multilayers May Inn Sim, Dickson Thian, Xiaoye Chen, Pin Ho, Hang Khume Tan, Chao Li, Ramu Maddu, Goolaup Sarjoosing, Nelson Lim Chee Beng, Sherry Lee Koon Yap, Anjan Soumyanarayanan Magnetic skyrmions (Sks) are topologically protected spin structures that exist at room temperature (RT) in multilayer (ML) magnetic films[1,2]. While Sks have promising current-driven motion in racetrack geometry, skyrmion Hall effect (SkHE) induced transverse deflection is an obstacle in fulfilling memory and computing applications[3]. Fortunately, antiferromagnetically (AF) coupled Sks do not exhibit SkHE[4], but conclusive experimental verifications of AF Sks in ML systems remain elusive. |
Tuesday, March 16, 2021 10:48AM - 11:00AM On Demand |
E40.00013: Reversible Skyrmion Logic System Xuan Hu, Maverick Chauwin, Felipe Garcia-Sanchez, Neilesh Betrabet, Alexandru Paler, Christoforos Moutafis, Joseph S. Friedman Magnetic skyrmions demonstrate exceptional potential as information carriers for next-generation computing systems in light of their topological stability, non-volatility, and small size. However, previous proposals for using skyrmions in logical computing systems have failed to take full advantage of the capabilities of skyrmions, and the lack of a cascading mechanism prevents their use in large-scale circuits. Here we propose a reversible skyrmion logic system with which we demonstrate a direct cascading mechanism, enabling a large-scale reversible skyrmion computing system [1]. This reversible computing system leverages the rich physics of magnetic skyrmions, including the spin-Hall effect, skyrmion-Hall effect, skyrmion-skyrmion repulsion, repulsion between skyrmions and the track boundaries, and electrical current-control of notch depinning. Furthermore, this proposed skyrmion logic increases the power efficiency by implementing the concept of reversible computing and eliminating skyrmion generation and destruction. Several Boolean logic functions and a cascaded full adder circuit are demonstrated to prove the feasibility of the proposed skyrmion logic system. |
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