Can immobile magnetic vortex nucleate a vortex-antivortex pair?

TL;DR

This paper demonstrates that an immobile magnetic vortex can nucleate a vortex-antivortex pair and switch polarity under a rotating magnetic field, challenging previous beliefs and using micromagnetic modeling and analytical methods.

Contribution

It shows that an immobile vortex can nucleate vortex-antivortex pairs and switch polarity under rotation, supported by micromagnetic simulations and analytical theory.

Findings

Vortex-antivortex pair nucleation occurs under rotating magnetic field.

Polarity switching is observed only in certain pinning conditions.

Dipole magnon mode softening explains dip creation mechanism.

Abstract

It is shown that under the action of rotating magnetic field an immobile vortex, contrary to a general belief, can nucleate a vortex-antivortex pair and switch its polarity. Two different kinds of OOMMF micromagnetic modeling are used: (i) the original vortex is pinned by the highly--anisotropic easy-axes impurity at the disk center, (ii) the vortex is pinned by artificially fixing the magnetization inside the vortex core in the planar vortex distribution. In both types of simulations a dip creation with a consequent vortex-antivortex pair nucleation is observed. Polarity switching occurs in the former case only. Our analytical approach is based on the transformation to the rotating frame of reference, both in the real space and in the magnetization space, and on the observation that the physical reason for the dip creation is softening of the dipole magnon mode due to magnetic field rotation.