Anisotropic Skyrmion Diffusion Controlled by Magnetic-Field-Induced Symmetry Breaking

Abstract

The diffusion of particles has wide repercussions, ranging from particle-based soft-matter systems to solid-state systems with particular electronic properties. Recently, in the field of magnetism, the diffusion of magnetic skyrmions, topologically stabilized quasiparticles, has been demonstrated. Here, we show that, by applying a magnetic in-plane field, and therefore, breaking the symmetry of the system, skyrmion diffusion becomes anisotropic, with faster diffusion parallel to the field axis and slower diffusion perpendicular to it. We furthermore show that the absolute value of the applied magnetic in-plane field controls the absolute values of the diffusion coefficients, so that one can thereby tune both the orientation of the diffusion and its strength. Based on the stochastic Thiele equation, we can explain the observed anisotropic diffusion as a result of the elliptical deformation of the skyrmions by the application of the in-plane field.

Magnetic-Field-Assisted Diffusion Motion of Magnetic Skyrmions

“…One can observe that, although the sizes of skyrmions perpendicular to the IP field change slightly, an obvious increase of their size that parallels the IP field leads to an increase of the size ratios, and that means an oval-shaped skyrmion structure observed on a two-dimensional surface. Note that an anisotropic skyrmion diffusion controlled by magnetic-field-induced symmetry breaking has been observed by Kerber et al 40 Here, we show a directed diffusion motion controlled by an IP field. We first determine the diffusion properties of the skyrmion by using a stable IP field.…”

Skyrmion Dynamics at Finite Temperatures: Beyond Thiele’s Equation

“…This approach has proven successful in describing the current-driven motion [16,17] of skyrmions, yielding quantitative agreement with numerical simulations at zero temperature. Furthermore, it leads to the prediction of skyrmion Brownian motion and the derivation of an analytic expression for the diffusion coefficients [18][19][20] whose validity in the high damping and/or low temperature regime was demonstrated using spin model simulations [21,22]. In experiments, however, the situation is frequently the opposite: the damping can be rather low and temperatures are usually rather high.…”

Universal Hopping Motion Protected by Structural Topology

“…The skyrmions react to SOT by moving in the current direction, simultaneously interacting with local pinning potentials (Figure 1e). The skyrmion paths and velocities are obtained by blob tracking technique, [28,[34][35][36] showing a stop-start motion, as shown in Figure 1f.…”