Intrinsic mechanism of nonlinear damping in magnetization reversal

The process of magnetization reversal in a fine ferromagnetic grain with a strong uniaxial anisotropy has been simulated for the case of an instantane ously applied reversal magnetic field. The "quasi" single-domain grain was considered as a system of 64 or 1000 subcubes coupled by exchange and dipol e-dipole interactions. The system of Landau-Lifshitz equations was numerica lly solved without any phenomenological damping terms. The dynamic process is characterized by a rapid magnetization reversal accompanied by a decreas e in the average magnetization. The system exhibits a nonlinear excitation of nonuniform magnetic oscillations (spin waves) driven by the uniform mode . We found limitations on magnetization reversal for small grain size and l arge applied field magnitude. The damping parameter has been obtained for s mall magnetization oscillations. (C) 2000 American Institute of Physics. [S 0021-8979(00)66008-5].