Low Temperature Anisotropy of Manganese-Iron Ferrites

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Abstract
The anisotropy of the composition system MnxFe3−xO4, 0.40≤x≤1.80, has been measured between 4.2° and 77°K by the torque method, supplementing previous measurements on this system by Penoyer and Shafer between 77° and 313°K. The anisotropy curves for 0.4≤x≤1.25 show a minimum below 110°K and appear to be the summation of a number of components of different sign and different temperature dependence—negative components which decrease in magnitude relatively slowly with increasing temperature and positive components which decrease more rapidly. Over most of the composition range studied K1 is negative at 4.2°K, but at x=0.80 the magnitude of the positive, low temperature contribution is sufficient to change the sign of K1 from negative to positive at 34°K. In the region x≤1.0, this contribution can be attributed to the presence of Fe2+ ions, but such an explanation is not applicable to the positive contributions observed in compositions for which x≥1.25 and in which there is no Fe2+. For 1.25≤x≤1.80, negative values of K1 at 4.2°K of unexpectedly large magnitude (<−3.7×105ergs/cm3) are observed. Unlike values at 77°K in this composition region, these values of K1 are of too large a magnitude to be attributed to the splitting of the 3d levels of Fe3+ ions in a cubic crystalline field.