Magnetic Anisotropy of Some Nickel Zinc Ferrite Crystals

Abstract

Single crystals of Ni_1−pZn_pFe₂O₄ (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.