Microwave polarizability of ferrite particles with non-uniform magnetization

The microwave permeability of composites made of ferrite particles in a non-magnetic matrix is affected by particle shape and size. To account for the second effect, we have developed a micromagnetic model for calculating the microwave polarizability of a particle with non-uniform magnetization. This model is described in detail: a generalized demagnetizing operator associated with the equilibrium magnetic configuration inside the particle is introduced; the polarizability is defined as the perturbation of this configuration by the external magnetic excitation; the permeability of a macroscopic sample is calculated using a space averaging procedure. The numerical methods are introduced and results for two systems are discussed: domain modes in thin films and ferrite composites with planar anisotropy. (C) 1999 Elsevier Science B.V. All rights reserved.