Current-driven skyrmion Depinning in Magnetic Granular Films

TL;DR

This paper investigates how disorder and grain boundaries in magnetic films influence the current-driven motion of skyrmions, revealing effects like enhanced Hall effect and size-dependent depinning, with implications for nanowire device design.

Contribution

It introduces a micromagnetic and phenomenological analysis of skyrmion depinning in granular films, highlighting disorder effects and size-dependent critical currents.

Findings

Disorder enhances the effective skyrmion Hall effect.

Critical current depends on grain size relative to skyrmion size.

Narrow nanowires exhibit higher skyrmion mobility.

Abstract

We consider current-driven motion of magnetic skyrmions in granular magnetic films. The study uses micromagnetic modeling and phenomenological analysis based on the Thiele formalism. Remarkably, disorder enhances the effective skyrmion Hall effect that depends on the magnitude of the driving force (current density and non-adiabaticity parameter). The origin is sliding motion of the skyrmion along the grain boundaries, followed by pinning and depinning at the grain junctions. A side-jump can occur during this depinning process. In addition, the critical current that triggers the skyrmion motion depends on the relative size of the crystallites with respect to the skyrmion size. Finally, when the skyrmion trajectory is confined along an edge by the non-adiabatic Magnus force, the critical current density can be significantly reduced. Our results imply that narrow nanowires have higher skyrmion mobilities.