Magnetic media switching dynamics in thermal equilibrium

Abstract

In high data rate magnetic recording it is important to have at least a simple model for the switching dynamics of the media magnetization. Using the Landau-L-lifshitz-Gilbert equation will not give switching when the applied field Hα and the anisotropy Hk line up, unless a small initial angle θi is introduced between magnetization and applied field. The media's switching speed now depends on θi and therefore becomes arbitrary. In reality, in thermal equilibrium, the media magnetization precesses noisily around some initial direction. This paper presents a closed-form expression for the ensemble average of this "thermally aided" switching. The expression can also be used to approximate media switching in the presence of demagnetization fields (thin-film media) and angular anisotropy distributions if one uses an "effective value" for the thermal stability factor KuV/kT.