A phenomenological model of magnetisation kinetics

Abstract

A magnetic equation of state or magnetic constitutive equation, in functional form H=H(M,M), has been developed by analogy with a mechanical constitutive equation of crystal plasticity. It is shown that magnetisation kinetics, i.e. the dependence of magnetisation on magnetic field and time, may be conveniently described in terms of solutions of the magnetic constitutive equation subject to given magnetic field constraints. Two experimental methods of investigating the phenomenon of magnetic viscosity, in which time variations of intensity of magnetisation are observed, are analysed. The results, from which magnetic viscosity parameters and hence values of the activation volumes involved in irreversible magnetisation processes are determined, are identical with the expressions previously derived in terms of activation energy distributions. The definitions of the magnetic susceptibilities involved in the earlier work are arbitrary; they are precisely defined in the present work.