Level intersection and instability of the magnetic structure in rare earth ferrite garnets

Magnetization anomalies observed for some mixed rare earth ferrite garnets in strong fields at low temperatures are theoretically investigated. A model is investigated in which the rare earth ions are treated in terms of the highly anisotropic Ising approximation. It is shown that for various orientations of the external magnetic field the instability resulting from intersection of rare earth ion ground levels possesses a fine structure. It reflects a detailed character of remagnetization of the rare earth ions located at various inequivalent positions. The magnetization curves of such a system are noted to be in a good agreement with experimental data available for holmium-yttrium iron garnets