Thermal motion of skyrmion arrays in granular films

Funding Information: This work was supported by the Academy of Finland (Grants No. 295269, No. 306978, and No. 327804), as well as by the Academy of Finland Centre of Excellence program Quantum Technology Finland (project 312298). We acknowledge the provision of computational resources by the Aalto Science-IT project. We thank See-Chen Ying, Ken Elder, and Enzo Granato for useful discussions. Publisher Copyright: © 2021 American Physical Society.Magnetic skyrmions are topologically distinct swirls of magnetic moments which display particlelike behavior, 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.Peer reviewe