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 as a system of n(= 2,4,8) subgrains with uniaxial anisotropy coupled by exchange interaction. The gyromagnetic equations of motion were solved without phenomenological damping terms. The evolution of the magnetization was found to exhibit nonlinear spin wave excitation on a short timescale. The average magnetization significantly decreases and demonstrates irregular oscillations 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, reassembled in a new equilibrium direction. (C) 1999 American Institute of Physics. [S0021-8979(99)40008-8].