Dynamic permeability in soft magnetic composite materials

This article reports on an isotropic model of the magnetic susceptibility b ased on an average field theory and proposes to predict the dynamic behavio rs of powder magnetic materials. It was essentially built around a so-calle d effective demagnetizing factor capable of taking the particle shapes into account. So, for a population of randomly distributed particles of anisotr opic shapes like, for instance, needles or flakes, we show that the effecti ve demagnetizing factor of this population of particles can be significantl y lowered with regard to the well known value of 1/3 classically used to re present the isotropy state. This phenomenon is interpreted as the natural t endency of particles to form clusters to which a moving demagnetizing facto r must be assigned. Taking then the aggregation process of particles into a ccount, the ability of the model to predict the dynamic properties of many composite magnetic materials is successfully demonstrated. Our development is illustrated by experimental results concerning a nickel-zinc ferrimagnet ic (Ni0.7Zn0.3Fe2O4) powder. (C) 2001 American Institute of Physics.