Néel‐Type Elliptical Skyrmions in a Laterally Asymmetric Magnetic Multilayer

Abstract

Magnetic skyrmions, topological chiral spin textures, have aroused extensive research interests due to their intriguing topology-related physics and promising applications in spintronic devices. [1-4] In most cases, skyrmions' chiral spin textures are mainly determined by the Dzyaloshinskii-Moriya interaction (DMI), [5-7] which favors a non-collinear spin configuration between neighboring spins. The appearance of DMI is a direct consequence of spin-orbit coupling and inversion symmetry breaking. [8-10] Depending on the structural symmetry of materials, DMI favors spin arrangement with specific symmetries. For example, natural inversion symmetry breaking in singlecrystal materials, such as MnSi, [11-13] FeCoSi, [14,15] FeGe, [16] and Cu 2 OSeO 3 , [17,18] leads to the emergence of bulk-type DMI Magnetic skyrmions, topological-chiral spin textures, have potential applications in next-generation high-density and energy-efficient spintronic devices for information storage and logic technologies. Tailoring the detailed spin textures of skyrmions is of pivotal importance for tuning skyrmion dynamics, which is one of the key factors for the design of skyrmionic devices. Here, the direct observation of parallel aligned elliptical magnetic skyrmions in Pt/Co/Ta multilayers with an oblique-angle deposited Co layer is reported. Domain wall velocity and spin-orbit-torque-induced out-of-plane effective field analysis demonstrate that the formation of unusual elliptical skyrmions is correlated to the anisotropic effective perpendicular magnetic anisotropy energy density (K eff u) and Dzyaloshinskii-Moriya interaction (DMI) in the film plane. Structural analysis and first-principles calculations further show that the anisotropic K eff u and DMI originate from the interfacial anisotropic strain introduced by the oblique-angle deposition. The work provides a method to tune the spin textures of skyrmions in magnetic multilayers and, thereby, a new degree of freedom for the design of skyrmionic devices.

DMI-Gradient-Driven Skyrmion Motion

“…This range covers the skyrmion stability region shown in Figure . The DMI gradient can be also introduced by creating composition gradients or strains induced at interfaces due to specific deposition approaches. , …”

“…The DMI gradient can be also introduced by creating composition gradients or strains induced at interfaces due to specific deposition approaches. 40,41 To characterize the DMI-gradient-driven motion, we compare it to the motion induced by a spin-polarized current. We place the skyrmion at the center of the stripe, with dimensions of 700 × 200 × 1 nm.…”

Elliptical skyrmions: theory and nucleation by a magnetic tip in an antiskyrmion-hosting material

“…Wilson et al 38 observed the distorted elliptical lattice state in the material Cu 2 OSeO 3 when the applied magnetic field was tilted with respect to the direction normal to the film. Cui et al 39 experimentally observed Néel-type elliptical skyrmions when they obliquely deposited one layer into a multilayer system.…”

Comprehensive Study of the Current-Induced Spin–Orbit Torque Perpendicular Effective Field in Asymmetric Multilayers

“…Thus, the magnetic configuration in the domain wall is ↑←↓, i.e., a left-handed chirality. The magnitude of DMI can be obtained by measuring the AHE loops of switching a Hall cross with combined H x and H z under a series of DC current densities [ 39 , 40 ]. Figure 2 d summarizes the SOT efficiency ( χ ) as a function of H x .…”