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 (Ni80Fe20) 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.