Theory of Magnetostriction in Cobalt-Manganese Ferrite

The magnetostrictive effect of an orbitally degenerate magnetic ion in a cubic ferromagnet is calculated in detail using crystal-field theory. In contrast to our previous work, it is not assumed that inter-atomic exchange energy is large compared with spin-orbit energy. The results are applied to the effect of cobalt in cobalt-manganese ferrite. It is found that the theory is consistent with experimental results for the magnetostrictive parameters λ₁₀₀ and λ₁₁₁ in the compound Co0.245{Mn}0.747Fe1.99{O}₄from 225^∘-355^∘K. By fitting theory to experiment, a trigonal splitting of about 630{cm}^{{-}1}$ for the ground state of the cobalt ion is inferred. The trigonal splitting has less than half its value in cobalt-iron ferrite.