Structure and induced anisotropy of new cobalt and manganese spinel defect ferrites

Directional ordering has been shown to increase the magnetic performance of magnetic recording particles. The results obtained on new materials synthesized to investigate and to use directional order (DO) effects are presented. These materials, spinel defect ferrites, contain cations in several valence states (Fe²⁺, Fe³⁺, Mn ²⁺, Mn³⁺, Mn⁴⁺). Results of structural analysis and the influence of the oxidation state and thermal treatment on the magnetic properties are discussed. It is concluded that mixed defect spinel ferrites substituted by high-valence-state manganese ions (3+, 4+) and cobalt make it possible to obtain very high coercivities for low cobalt content (4.5%). Moreover, these materials present no aging effect. The extensive increase of the coercivity is due to the induced anisotropy by DO. The experimental results are interpreted according to the Neel model