Thermal motion of skyrmion arrays in granular films

TL;DR

This study investigates how grain boundaries in granular films influence the thermally-driven diffusion of skyrmions, revealing two distinct regimes of interaction that affect their mobility and clustering behavior.

Contribution

It provides new insights into the interaction between skyrmions and grain boundaries, highlighting the impact on skyrmion diffusion and clustering in granular magnetic films.

Findings

Grain boundaries reduce skyrmion diffusion at longer times for certain grain sizes.

Grain boundaries enhance effective diffusion at shorter times due to gyrotropic motion.

Skyrmion clustering occurs in grains with lower magnetic anisotropy for larger grain sizes.

Abstract

Magnetic skyrmions are topologically-distinct swirls of magnetic moments which display particle-like behaviour, including the ability to undergo thermally-driven diffusion. In this paper we study the thermally activated motion of arrays of skyrmions using temperature dependent micromagnetic simulations where the skyrmions form spontaneously. In particular, we study the interaction of skyrmions with grain boundaries, which are a typical feature of sputtered ultrathin films used in experimental devices. We find the interactions lead to two distinct regimes. For longer lag times the grains lead to a reduction in the diffusion coefficient, which is strongest for grain sizes similar to the skyrmion diameter. At shorter lag times the presence of grains enhances the effective diffusion coefficient due to the gyrotropic motion of the skyrmions induced by their interactions with grain boundaries. For grain sizes significantly larger than the skyrmion diameter clustering of the skyrmions occurs in grains with lower magnetic anisotropy.