Magnetocrystalline Anisotropy of Mg–Fe Ferrites: Temperature Dependence, Ionic Distribution Effects, and the Crystalline Field Model

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Abstract
The magnetocrystalline anisotropy constant (K1) and saturation magnetization (Ms) of magnesium‐iron ferrite monocrystals containing 6 to 50 mole percent magnetite were measured as a function of temperature (T) and ionic distribution. For crystals containing 6 to 25 mole percent magnetite, K1 was found to vary more rapidly with temperature when the ionic distribution in a crystal corresponds to a relatively high Ms than when it corresponds to a relatively low Ms in the same crystal. The observed changes in K1 resulting from alterations of the ionic distribution are shown to be consistent with a phenomenological one‐ion anisotropy model. On this basis, the measurements yield a positive anisotropy for a ferric ion in a tetrahedral site (A) and a negative anisotropy for this ion in an octahedral site (B). Finally, the data obtained on one Mg‐Fe ferrite crystal (containing 6 mole percent magnetite) were used in the Yosida‐Tachiki anisotropy theory. The ferric ion cubic crystalline field splitting parameters aA and aB occurring in this theory were determined for two different states of ionic distribution in the crystal. It was found that aA = −0.0092 cm−1 and aB = +0.0232 cm−1 for the state corresponding to a relatively high Ms, and aA = −0.0135 cm−1 and aB = +0.0250 cm−1 for the state corresponding to a relatively low Ms. The theoretical anisotropy curves obtained by using these a values are in very good agreement with experiment. Furthermore, the aB values agree with aB = +0.0205 cm−1 determined by Low from paramagnetic resonance measurements on ferric ions in MgO.

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