Chemical Inhomogeneities and Square B-H Loops

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Abstract
It is shown that in ferrites exhibiting spontaneously square B‐H loops, reverse‐domain nucleation may occur either at a grain boundary or at a chemical inhomogeneity having a volume roughly 0.1 of a grain volume, a magnetization about 2% different from that of the parent matrix, and no static crystallographic discontinuity at the inhomogeneity‐matrix interface. It is pointed out that such chemical inhomogeneities may occur in spinels having Jahn‐Teller ions in concentrations that are too small to produce a cooperative, static distortion of the entire crystal from cubic symmetry. It is postulated that the formation of such inhomogeneities is responsible for the sharp knee in spontaneously square B‐H loops found in many ferrites containing Mn3+ and Cu2+ ions, in particular the magnesium‐manganese composition used in memory‐core ferrites.