MICROMAGNETIC THEORY OF NONUNIFORM MAGNETIZATION PROCESSES IN MAGNETIC RECORDING PARTICLES

Recent micromagnetic results are discussed from a unified point of view. Emphasis is placed on a reorientation of the focus of micromagnetic theory towards a dynamical treatment of the magnetization processes in non-uniformly magnetized particles. The theory requires merely the knowledge of the micromagnetic energy functional and the prescription for the dynamical evolution equations. It is demonstrated that the dynamical aspects are especially important during irreversible switching. In the micromagnetic calculations of this paper the Landau-Lifshitz equations are taken as the evolution equations for irreversible switching. The distinction of reversible and irreversible processes leads to a rigorous definition of the notion of switching field. This yields a generalization of the classical nucleation field. In this context it is also necessary to carefully distinguish between equilibrium magnetization configurations and transient magnetization configurations. The latter magnetization states represent the non-linear dynamical generalizations of the classical nucleation modes. It is demonstrated from first principles that both the equilibrium states and the transient states can be described in simple topological terms for a wide range of magnetic particles as used in magnetic recording technology.