Adiabatic dynamics of small ferromagnetic particles

Abstract

The purpose of this work is to present an analytical description of dynamics of small ferromagnetic particles (SFP) with uniaxial anisotropy energy and slowly varying magnetic field applied at an arbitrary angle to it. Theoretical analysis based on the consideration of the Landau–Lifshits–Gilbert (LLG) equation employs an asymptotic expansion similar to the famous semiclassical WKBJ solution of quantum mechanics equations. The small parameter of the expansion is the ratio of characteristic frequency of the applied magnetic field to the precession frequency. The equation describing slow dynamics of SFP is derived. Different cases of slow variation of magnitude and direction of magnetic field are considered. The formal solution of linearized equations is obtained and exact solutions are presented in the cases of magnetic field parallel and perpendicular to the anisotropy axis.