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Single crystals of Ni1−pZnpFe2O4 (p=0.20 and 0.65) were prepared from a melt in a PbO:B2O3 flux. The anisotropy constant K1 was deduced from torque measurements in a (100) plane. | K1 | increases linearly with p at low temperatures. Combining the results with data on p=0 and p=0.33 from the literature, one can represent K1 at 4°K as the sum of contributions from tetrahedral Fe3+ (+0.04 cm−1 per ion) and octahedral Fe3+ (−0.07 cm−1) in agreement with data on other iron spinels. The temperature, dependence of K1 for p=0.65 agrees with Wolf's expectations for ferrimagnets with a weak exchange. Above room temperature the torque curves for this sample show a spurious uniaxial term, increasing with temperature. Both K1 and this extra torque are reduced by increasing the external field.

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