Gyrotropic mode frequency of vortex-state permalloy disks

Abstract

Submicron permalloy magnetic dots have a vortex ground state because of competition between the exchange and magnetostatic interactions, and the application of an in-plane magnetic pulse will result in precession of the vortex about the dot axis at a frequency in the sub-GHz range. The precession frequency of this mode is calculated using a perturbation technique based on vortex–magnon scattering including the magnetostatic interaction. These calculations show that the frequencies vary between 0.2 and 0.8 GHz for 60 nm disks or radii between 250 nm and 1000 nm, which agrees with recent experimental data.