Anisotropy of Manganese-Substituted Cobalt Ferrite

Study of the anisotropy of magnetostrictive cobalt ferrite composites and its temperature dependence helps better understand the magnetomechanical properties, which will allow tuning the properties of the materials for magnetoelastic stress and torque sensors applications. We have investigated the temperature dependence of anisotropy of Mn-substituted cobalt ferrite CoMn$_{x}$Fe$_{2-x}$O$_{4}$ (0~$\le $~x~$\le $~0.8). Magnetization measurements of the hysteresis loops were made at temperatures over the range 200-300 K using a SQUID magnetometer. To determine the anisotropy constant $K_{1}$, the high field regime of the loops was fitted using the law of approach approximation $M(T)$~=~$M_{s}\cdot $(1-\textit{$\alpha $K}$_{1}^{2}$/$H^{2})$, where $\alpha $~=~8/105~\textit{$\mu $}$_{0}^{-2}M_{s}^{-2}$ for the samples which have spinel structure and cubic anisotropy. It was found that anisotropy decreases with increasing Mn content and with increasing temperature for all compositions. However, at higher temperatures the anisotropy of the Mn-substituted specimens converges to approximately the same value $K_{1}$=200 kJ/m$^{3}$. The pure cobalt ferrite sample appears to have considerably higher anisotropy $K_{1}$ than the Mn-substituted samples over the whole temperature range.