Magnus-induced dynamics of driven skyrmions on a quasi-one-dimensional periodic substrate

Abstract

We numerically examine driven skyrmions interacting with a periodic quasi-one dimensional substrate where the driving force is applied either parallel or perpendicular to the substrate periodicity direction. For perpendicular driving, the particles in a purely overdamped system simply slide along the substrate minima; however, for skyrmions where the Magnus force is relevant, we find that a rich variety of dynamics can arise. In the single skyrmion limit, the skyrmion motion is locked along the driving or longitudinal direction for low drives, while at higher drives a transition occurs to a state in which the skyrmion moves both transverse and longitudinal to the driving direction. Within the longitudinally locked phase we find a pronounced speed up effect that occurs when the Magnus force aligns with the external driving force, while at the transition to transverse and longitudinal motion, the skyrmion velocity drops, producing negative differential conductivity. For collectively interacting skyrmion assemblies, the speed up effect is still present and we observe a number of distinct dynamical phases, including a sliding smectic phase, a disordered or moving liquid phase, a moving hexatic phase, and a moving crystal phase. The transitions between the dynamic phases produce distinct features in the structure of the skyrmion lattice and in the velocity-force curves. We map these different phases as a function of the ratio of the Magnus term to the dissipative term, the substrate strength, the commensurability ratio, and the magnitude of the driving force.

Pinning of magnetic skyrmions in a monolayer Co film on Pt(111): Theoretical characterization and exemplified utilization

“…Since we have focused most of our analysis so far on point-localized defects, we next discuss the pinning behavior of skyrmions on extended defects where material properties are changed. We first consider the motion of an isolated skyrmion along a linear defect [40][41][42][43] (a narrow strip with a varied material parameter) to be used in, e.g., racetrack memories [see Figs. 12(a)-12(c)].…”

“…Other theoretical works [10,18,[28][29][30] have studied the dynamical behavior of skyrmions around a defect, but could not quantify the exact transition from a pinned to an unpinned state. There are also a number of works in the literature that have considered skyrmion behavior in periodic [34,35] and random [36][37][38] pinning arrays, ratchet geometries [39], and linear defects [40][41][42][43]. However, these works typically assume a phenomenological model for pinning (effective parabolic potentials) rather than a microscopically justified one.…”

Skyrmion Dynamics and Topological Sorting on Periodic Obstacle Arrays

“…Due to their stability, size scale, and manipulability, skyrmions are very promising candidates for a variety of applications including memory, logic devices, and alternative computing architectures [49,50]. The capability to precisely control the direction, traversal distance, and reversibility of skyrmion motion could open up new ways to create such devices, and there are already a number of proposals for controlling skyrmion motion using structured substrates such as race tracks [49,51,52], periodic modulations [53], or specially designed pinning structures [54,55,56,57,58]. One proposal for controlling skyrmion motion involves having the skyrmions interact with a two dimensional periodic substrate of the type that has already been realized for colloidal particles and vortices in type-II superconductors, and there are existing experimental realizations of skyrmions interacting with two-dimensional (2D) antidot arrays [59].…”

Chiral edge currents for ac-driven skyrmions in confined pinning geometries

“…We model the skyrmions using a particle based approach for skyrmions interacting with pinning as employed previously [40,41,[61][62][63][64].…”