Thermally Activated Decay of Magnetic Vortices

We experimentally probe thermally activated decay of magnetic vortices, by observing annihilations within an array of Ni$_{80} $Fe$_{20}$ discs through hysteresis measurements. Specifically, the statistics of vortex annihilation are mapped as a function of the magnitude of, and the dwell time at, the peak fields applied during hysteresis scans. Magnetic vortices in micro- and nano-scale thin film ferromagnetic elements exhibit interesting and complex behavior. Demagnetization interactions make understanding processes like the annihilation of a vortex during magnetic switching challenging. Recent work has shown that the annihilation process can take place over an extended period of time\footnote{Z. Liu, R.D. Sydora and M.R. Freeman, PRB 77, 174410 (2008).} implying that there is a characteristic decay process, likely thermally governed. Through application of an Arrhenius model we extract information about the energy barrier preventing decay, and hence information about the energetic contributions of the demagnetization effects. We anticipate that this information will be useful in extending analytical models of magnetic vortices.