Sublattice Rotations in Ferrimagnets: The Case of Pyrrhotite

Abstract

The molecular field model is used to analyze the sublattice rotations in a uniaxial two sublattice ferrimagnet, towards absolute saturation. In the particular case K, K′ <0 and (2K/M) + (2K′/M′) < −n (M1/2−M′1/2)2 with the field applied along the crystal axis, the two sublattices rotate directly towards absolute saturation with χ≃1/n as susceptibility. This model applies to pyrrhotite, Fe7S8, and explains its paramagnetic behavior along the hard axis, along with the simultaneous existence of a small spontaneous magnetization in the easy plane.