Polarisation selective magnetic vortex dynamics and core reversal in rotating magnetic fields

TL;DR

This study demonstrates that rotating magnetic fields can selectively excite and reverse the vortex core in magnetic vortices, revealing polarization-dependent dynamics through time-resolved imaging.

Contribution

It introduces the observation of polarization-selective vortex dynamics and core reversal driven by rotating magnetic fields, a novel control mechanism.

Findings

Rotating fields excite vortex gyrotropic modes only when their rotation sense matches the vortex gyration.

Rotating magnetic fields can selectively reverse the vortex core polarization.

Time-resolved X-ray microscopy visualizes the vortex response to rotating fields.

Abstract

A magnetic vortex occurs as an equilibrium configuration in thin ferromagnetic platelets of micron and sub-micron size and is characterised by an in-plane curling magnetisation. At the centre, a magnetic singularity is avoided by an out-of-plane magnetisation core. This core has a gyrotropic excitation mode, which corresponds to a circular motion of the vortex around its equilibrium position, where the rotation sense is determined by the direction of the vortex core magnetisation, its polarisation. Unlike linear fields or spin polarised currents, which excite both polarisation states, an in-plane rotating field can selectively excite one of the polarisation states. Here we report the observation of vortex dynamics in response to rotating magnetic fields, imaged with time-resolved scanning X-ray microscopy. We demonstrate that the rotating field only excites the gyrotropic mode if the rotation sense of the field coincides with the vortex gyration sense and that such a field can selectively reverse the vortex polarisation.