Capturing of a Magnetic Skyrmion with a Hole

TL;DR

This study combines analytical and numerical methods to explore how magnetic skyrmions interact with holes in chiral magnets, revealing conditions for pinning, depinning, and the effects of defects on skyrmion dynamics.

Contribution

It provides a detailed analysis of skyrmion-hole interactions, including effective potential modeling and the impact of current density and magnetic field variations.

Findings

Skyrmions can be captured by holes at intermediate current densities.

The maximum capture cross section scales with the skyrmion radius and sqrt of damping.

Small defect densities can accelerate skyrmion motion and induce a Hall effect.

Abstract

Magnetic whirls in chiral magnets, so-called skyrmions, can be manipulated by ultrasmall current densities. Here we study both analytically and numerically the interactions of a single skyrmion in two dimensions with a small hole in the magnetic layer. Results from micromagnetic simulations are in good agreement with effective equations of motion obtained from a generalization of the Thiele approach. Skyrmion-defect interactions are described by an effective potential with both repulsive and attractive components. For small current densities a previously pinned skyrmion stays pinned whereas an unpinned skyrmion moves around the impurities and never gets captured. For higher current densities, j_c1 < j < j_c2, however, single holes are able to capture moving skyrmions. The maximal cross section is proportional to the skyrmion radius and to Sqrt(alpha), where alpha is the Gilbert damping. For j > j_c2 all skyrmions are depinned. Small changes of the magnetic field strongly change the pinning properties, one can even reach a regime without pinning, j_c2=0. We also show that a small density of holes can effectively accelerate the motion of the skyrmion and introduce a Hall effect for the skyrmion.