The influence of chemistry onB/Hloop shape, coercivity and flux-reversal time in ferrites

Abstract

The factors which influence the shape of the B/H loop, the coercivity, the permeability and the flux-reversal time in ferrimagnetic spinels are considered on two levels; a macroscopic and an atomic level. To minimize consideration of shape-dependent properties, the ferrite components are assumed to be toroids. With the assumption that domain walls are present in the material, coercivity, permeability, flux reversal and the influence of grain-boundary magnetic poles on B/H loop shape are determined in terms of measurable physical parameters of the material. From these relationships it is possible for the design engineer to determine the optimum parameters for a given application. The spinel-like magnetic oxides may, to the first approximation, be considered as ionic lattices. In order to obtain some insight into the control of the macroscopically measurable physical parameters by chemical composition and preparation procedures, as a second approximation the directional character of the ionic orbitals is emphasized to describe the influence of covalent effects on magnetic moment, magnetic exchange, and crystalline anisotropy. These effects are applied theoretically to the cations of particular interest in ferrites. Finally, some properties of several ferrites are displayed graphically to illustrate the importance of processing and chemistry on the magnetic character of ferrospinels.