On the magnetocrystalline anisotropy of nickel-iron ferrites

In order to determine regularities in the temperature dependence of the magnetocrystalline anisotropy of nickel-iron ferrites, studies of single-crystal spheres of these ferrites of various compositions were made by the torque method. It was established that the function K₁ (T) is affected by the presence of ions of bivalent iron (the presence of cobalt ions in the samples or in the charge was not detected by either chemical or x-ray methods). In the absence of ions of bivalent iron, K₁ decreases in absolute value with rise in temperature, always remaining negative. With increased concentrations of Fe² ions, K₁ can have a positive sign at high and low temperatures, and a negative sign in the intermediate temperature range.The function K₁(T) is affected by initial brief high-temperature (900 ° C, 2 hr) and prolonged low-temperature (300–350 ° C, 2 days) heat treatment of the single crystals. It was established that the heat treatments also affect other magnetic and electric properties of the single crystals studied.