Magnetic media switching dynamics in thermal equilibrium

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-Lifshitz-Gilbert equation will not give switching when the applied field H, and the anisotropy H_k line up, unless a small initial angle θ_i is introduced between magnetization and applied field. The media´s switching speed now depends on θ_i 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 K_u V/kT