Vortex Polarity Switching in Magnets with Surface Anisotropy

TL;DR

This paper investigates how surface anisotropy influences vortex core reversal in magnetic particles, revealing deformation-dependent switching mechanisms and singularity types, supported by simulations and analytical models.

Contribution

It introduces a detailed analysis of vortex polarity switching influenced by surface anisotropy, including a simple analytical model and simulation validation.

Findings

Vortex core deformation depends on surface anisotropy type.

Switching involves different singularity types: linear or point.

Analytical and simulation results agree on switching mechanisms.

Abstract

Vortex core reversal in magnetic particle is essentially influenced by a surface anisotropy. Under the action of a perpendicular static magnetic field the vortex core undergoes a shape deformationof pillow- or barrel-shaped type, depending on the type of the surface anisotropy. This deformation plays a key point in the switching mechanism: We predict that the vortex polarity switching is accompanied (i) by a linear singularity in case of Heisenberg magnet with bulk anisotropy only and (ii) by a point singularities in case of surface anisotropy or exchange anisotropy. We study in details the switching process using spin-lattice simulations and propose a simple analytical description using a wired core model, which provides an adequate description of the Bloch point statics, its dynamics and the Bloch point mediated switching process. Our analytical predictions are confirmed by spin-lattice simulations for Heisenberg magnet and micromagnetic simulations for nanomagnet with account of a dipolar interaction.