抄録
The uniaxial anisotropy induced by the magnetic annealing in both single and poly-crystals of iron-cobalt ferrites has been studied experimentally. It is shown that the magnitudes of the uniaxial anisotropy depend essentially on the degree of oxidation of the specimens and become almost zero after deoxidizing heat treatments. Contrary to the conclusion by Bozorth et al., the dependence of the magnitude of the uniaxial anisotropy on the direction of the annealing magnetic field is observed for a cobalt rich single crystal, showing a maximum along ⟨100⟩ and a minimum along ⟨110⟩ in (001) plane. Relaxation behaviour of the uniaxial anisotropy is studied by measuring directly the change of torque at high temperatures (240°C∼350°C) with a polycrystalline cobalt ferrite. It has been found that the results can be described by a simple empirical formula, supporting that the magnetic annealing effect has no critical temperature. The variation of electrical conductivity with temperature has also no anomaly at the effective temperature range.
Considering all the experimental results obtained, we have reached the conclusion that the uniaxial anisotropy in these ferrites is due to the presence of directional short range order among various cations and cation vacancies in the spinel matrix. The nearest neighbour pair of a cobalt ion and a vacancy seems to play a principal role in this mechanism.
