Temperature dependence of magnetic anisotropy in Mn-substituted cobalt ferrite

The temperature variation of magnetic anisotropy and coercive field of magnetoelastic manganese-substituted cobalt ferrites ( Co Mn x Fe 2 − x O 4 with 0 ⩽ x ⩽ 0.6 ) was investigated. Major magnetic hysteresis loops were measured for each sample at temperatures over the range 10-400 K, using a superconducting quantum interference device magnetometer. The high-field regimes of the hysteresis loops were modeled using the law of approach to saturation equation, based on the assumption that at sufficiently high field only rotational processes remain, with an additional forced magnetization term that was linear with applied field. The cubic anisotropy constant K 1 was calculated from the fitting of the data to the theoretical equation. It was found that anisotropy increases substantially with decreasing temperature from 400 to 150 K, and decreases with increasing Mn content. Below 150 K, it appears that even under a maximum applied field of 5 T, the anisotropy of Co Fe 2 O 4 and Co Mn 0.2 Fe 1.8 O 4 is so high as to prevent complete approach to saturation, thereby making the use of the law of approach questionable in these cases.