Generalizations of Snoek equation for anisotropic media with magnetic relaxation

Abstract

Using the general methods of non-equilibrium thermodynamics, a theory for anisotropic magnetizable media in which magnetic relaxation phenomena occur is formulated. In this paper, some results are revised, some others are new. First, a critical revision is given in the case where it is assumed that n microscopic phenomena give rise to magnetic relaxation, and the contributions of these phenomena to the macroscopic magnetization are introduced as internal variables in the Gibbs relation. Phenomenological equations and linear state equations are formulated, and magnetic relaxation equations generalizing Snoek equation are obtained. Then, new results are derived in the special case where all cross-effects are neglected, except for possible effects among the different types of magnetic relaxation phenomena, and by direct computations, generalized Snoek equations are worked out when the magnetization axial vector is additively composed of two irreversible parts, and in the case of anisotropic Snoek media and anisotropic De Groot–Mazur media. Also, particular results are presented and reviewed in the cases where the considered media have symmetry properties, under orthogonal transformations, which are i) invariant with respect to all the rotations of the frame of axes; ii) invariant with respect to all the rotations and inversions of the frame of axes.