The properties of magnetic mixtures with particular reference to the naturally occurring ironsands

Abstract

Results on the relation between volume content of magnetic material and the resultant permeability of magnetic mixtures in which the magnetic particles are (1) arranged in a regular rectangular lattice and (2) dispersed randomly throughout the mixture, are described. The results show that the first case is adequately described by Rayleigh's equation and that this can be simplified to Maxwell's equation for a cubic arrangement of spheres provided the volume ratio is small. The second case, i.e. of randomly dispersed particles is investigated by experiments on ironsand mixtures. In this case the particles are not true spheres but it is shown that Fricke's equation, an extension of Maxwell's equation to the case of spheroids, adequately describes the behaviour of the mixture. The dependence of the 'form factor' occuring in this equation on the alignment of the particles and the applied field is investigated and the possibility of using the results to predict the amount of iron ore present in a magnetite deposit discussed.