1ST-PASSAGE-TIME APPROACH TO OVERBARRIER RELAXATION OF MAGNETIZATION

We consider the irreversible dynamics of the magnetization vector M in a single-domain particle. The dynamics is given by a stochastic phenomenological equation due to Gilbert. It contains a damping field proportional to M and a corresponding white noise field component. The probability distribution function satisfies a Fokker-Planck equation derived by Brown. We give the overbarrier decay rate κ out of a metastable minimum. First we rederive the well-known expression for κ for an axially symmetric model. We argue that this result is unphysical. For systems of general point symmetry of the magnetic anisotropy energy we give κ in both the low-damping and intermediate- to high-damping limits. © 1990 Plenum Publishing Corporation.