Magnetic Properties of Cobalt-Substituted Ni–Zn Ferrites

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Abstract
The imaginary part µ'' of the complex magnetic permeability \hatµ (\hatµ=µ'-jµ'') was found to be linearly related to the real part µ' for cobalt-substituted ferrites with the same composition which were annealed at 280°C for various kinds of hours. This fact is explained by assuming that the imaginary part is associated with wall displacement and the contribution of this process to µ' is related to the value of induced anisotropy which is different among specimens heat-treated differently. Two peaks of the imaginary part µ'' were observed in magnetic spectra for the AC demagnetized specimens. The low frequency peak is ascribed to the resonance of domain walls which were displaced from their stable positions. Abrupt increase of the imaginary part µ'' and disappearance of constricted loops were observed at low temperatures, which are explained in terms of the change in sign of the cubic crystalline anisotropy constant K 1.