Clogging, Diode and Collective Effects of Skyrmions in Funnel Geometries

Abstract

Using a particle-based model, we examine the collective dynamics of skyrmions interacting with a funnel potential under dc driving as the skyrmion density and relative strength of the Magnus and damping terms are varied. For driving in the easy direction, we find that increasing the skyrmion density reduces the average skyrmion velocity due to jamming of skyrmions near the funnel opening, while the Magnus force causes skyrmions to accumulate on one side of the funnel array. For driving in the hard direction, there is a critical skyrmion density below which the skyrmions become trapped. Above this critical value, a clogging effect appears with multiple depinning and repinning states where the skyrmions can rearrange into different clogged configurations, while at higher drives, the velocity-force curves become continuous. When skyrmions pile up near the funnel opening, the effective size of the opening is reduced and the passage of other skyrmions is blocked by the repulsive skyrmion-skyrmion interactions. We observe a strong diode effect in which the critical depinning force is higher and the velocity response is smaller for hard direction driving. As the ratio of Magnus force to dissipative term is varied, the skyrmion velocity varies in a non-linear and non-monotonic way due to the pile up of skyrmions on one side of the funnels. At high Magnus forces, the clogging effect for hard direction driving is diminished.

Current-Induced Helicity Switching of Frustrated Skyrmions on a Square-Grid Obstacle Pattern

“…However, skyrmions could be destroyed by touching the edge. Recently, it has been shown that a more effective strategy to confine, protect, and control skyrmions in magnetic thin films is to construct defect lines with different magnetic properties [63][64][65][66][67][68][69][70][71][72][73][74] , which can be realized in engineered multilayer nanostructures 75) or by using focused irradiation 76) . However, the helicity dynamics of a frustrated skyrmion confined by defect lines have not yet been explored.…”

Particle-like skyrmions interacting with a funnel obstacle

“…In magnetic systems, funnel obstacles or pinning barriers may also affect the dynamics of particle-like skyrmions driven by external forces. For example, the dynamics of a single skyrmion or multiple skyrmions can be effectively modified using an array of funnel barriers [39,40], which could lead to the clogging, diode, and collective effects of skyrmions. However, there are still many open questions in the complex dynamics of multiple skyrmions interacting with funnel obstacles.…”