Micromagnetic grain as a nonlinear oscillator

A new theoretical approach is considered to analyse the behaviour of micromagnetic grains. The coherent rotation of magnetizations is represented as dynamics of a nonlinear oscillator. The Langevin equations are introduced to study the role of thermal fluctuations and the corresponding Fokker–Planck equation is obtained. It is shown that the conventional Landau–Lifshitz–Gilbert damping is consistent with thermodynamics only for small deviations of magnetization from the equilibrium state. The mean first passage time from the initial potential well is calculated.