Properties of electromagnetic waves in ferrites

Abstract
In this paper we present a derivation of the general wave equation governing the propagation of electromagnetic waves in ferrites. This is shown to be equivalent to the usual Helmholtz form obtained by introducing a permeability tensor. Its real underlying structure is somewhat obscured by the Helmholtz form because in this form the time dependence is submerged in the frequency-dependent elements of the permeability tensor. However, the main purpose of the paper is to provide a systematic account of the properties of electromagnetic waves in ferrites and this is done by making use of the close analogy that exists between wave propagation in ferrites and that in cold magnetized plasmas. This facilitates the construction of a so-called ‘C. M. A. diagram’ for a ferrite, which classifies the waves according to the various topologies of the refractive index and ray surfaces (along with the associated wave polarizations) in a two-dimensional parameter space that relates the wave frequency to the precessional frequencies intrinsic to the magnetization of the ferrite. The insight into the behaviour of waves in ferrites that this approach provides is illustrated in connection with the phenomena of cut-offs, resonances and wave-focusing, which give rise to caustics.

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