Induced Anisotropy in Iron-Deficient Ni-Co Ferrites at Low Temperatures

Abstract

The anisotropy Ku at −183°C in iron-deficient Ni-Co ferrites cooled down from room temperature in magnetic field is observed. It increases rapidly with decreasing contents of Fe₂O₃ and seems to attain a saturation value at a certain value of Fe₂O₃ contents. It also increases approximately in proportion to Co concentration. The activation energy for this process is about 0.25 to 0.4 eV. This anisotropy has been explained in terms of the preferential occupation of Co³⁺ ions in the four kinds of 16d sites arising from electron migration between Co²⁺ and Co³⁺ ions. The anisotropy Ku is not observed in iron deficient Mg-, Mn-, and Cu- ferrites containing a small amount of Co.