Magnetic media switching dynamics in thermal equilibrium

In high data rate magnetic recording it is important to have at least a sim ple model for the switching dynamics of the media magnetization. Using the Landau-Lifshitz-Gilbert equation will not give switching when the applied f ield H-a and the anisotropy H-k line up, unless a small initial angle theta (i) is introduced between magnetization and applied field. The media's swi tching speed now depends on theta (i) and therefore becomes arbitrary. In r eality, in thermal equilibrium, the media magnetization precesses noisily a round some initial direction. This paper presents a closed-form expression for the ensemble average of this "thermally aided" switching. The expressio n can also be used to approximate media switching in the presence of demagn etization fields (thin-film media) and angular anisotropy distributions if one uses an "effective value" for the thermal stability factor KuV/kT.