Factors affecting initial permeability of Co-substituted Ni-Zn-Cu ferrites

Iron deficient compositions of (Ni_0.2Cu_0.2Zn _0.6)_1.02xCo_xFe_1.98O₄ (0⩽x⩽0.05) were prepared to investigate their initial permeability dependence on cobalt contents. Extrinsic factors such as grain size and sintered density change little in samples sintered at 900°C, so their effects on permeability can be neglected. Intrinsic factors such as saturation magnetization, magnetocrystalline anisotropy (K₁) and magnetoelastic anisotropy (K_σ) can not account for the variation of initial permeability with Co content. Measurement of thermoelectric power shows that the concentration of cation vacancies increases with Co content. Therefore, the local induced anisotropy increases by the ordering of Co ions via increased cation vacancy concentration. This increase in induced anisotropy results in the decrease of initial permeability