Thermal reversal of magnetization as "random walk" dynamics of a nonlinear oscillator

Abstract

Coherent rotation of magnetization in a grain is represented as the dynamics of a nonlinear oscillator excited by random force. A stochastic differential equation is introduced to study the role of thermal fluctuations and the corresponding Fokker-Planck equation is obtained. It is shown that conventional Landau-Lifshitz-Gilbert damping is consistent with thermodynamics only for small deviations of the magnetization from the equilibrium state. An exact formula for the first passage time from the initial potential well is obtained. © 1999 American Institute of Physics.