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/sub k/ line up, unless a small initial angle /spl theta//sub i/ is introduced between magnetization and applied field. The media's switching speed now depends on /spl theta//sub 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/sub u/V/kT.