Magnetization reversal as a nonlinear multimode process

Dynamic magnetization reversal has been simulated in a single grain for an instantaneously applied reversal magnetic field. The grain was considered a s a system of n(= 2,4,8) subgrains with uniaxial anisotropy coupled by exch ange interaction. The gyromagnetic equations of motion were solved without phenomenological damping terms. The evolution of the magnetization was foun d to exhibit nonlinear spin wave excitation on a short timescale. The avera ge magnetization significantly decreases and demonstrates irregular oscilla tions at a well defined mean value. The final stage of reversal is the spin -lattice damping on a longer time scale. The magnetic moment is, thereby, r eassembled in a new equilibrium direction. (C) 1999 American Institute of P hysics. [S0021-8979(99)40008-8].