Phase diagram of magnetic vortex dynamics

The dynamics of a magnetic vortex are influenced profoundly by nonlinear effects at large and small amplitudes. For example, a strongly driven magnetic vortex is unstable with respect to internal deformation, leading to reversal of its core magnetization. At small amplitudes, a nonlinear response is associated with pinning of the vortex core. Given these phenomena, there is an acute need for a global picture of vortex dynamics over a wide range of excitation amplitudes and frequencies. We have constructed a phase diagram of vortex dynamics in permalloy (Ni ₈₀Fe ₂₀) disks by probing the response spectrum over four orders of magnitude in excitation power. We identify the boundary separating pinned and unpinned dynamics in a phase space of amplitude and frequency. Our approach allows for a highly quantitative analysis of the pinning potential for localized defects and can be used to trace the dynamics of a single vortex from deep in the pinning regime to the onset of core reversal.