Excitation of vortex core gyration in nanopillars through driven Floquet magnons

Abstract

The dynamics of vortex states in confined geometries like thin-film disks are characterized by a sub-GHz gyration, representing the damped oscillatory motion of the vortex core about the disk center. It has recently been shown that interactions between the core and azimuthal spin waves, lying in the GHz range and driven by magnetic fields, can result in steady-state core gyration. The gyration in turn provides a time-periodic modulation for the spin waves, resulting in the emergence of Floquet states. Here, we present results of a theoretical and computational study in which we examine how Floquet modes sustain this core gyration. In particular, we find that multiple steady-state gyration radii are possible under certain field conditions, resulting from the nonlinear interactions between the core and Floquet modes. Different gyration radii result in distinct Floquet frequency comb spectra and allow for hysteretic effects, as reported in recent experiments.