Studies on the magnetic anisotropy and the coercivity of granular gamma-Fe2O3 powders

The granular gamma-Fe2O3 powders are prepared. The particle shapes and mean particle sizes of the samples are determined by Transmission Electron Microscopy (TEM). Using Extracting Sample Magnetometer (ESM) and Vibrating Sample Magnetometer (VSM); the magnetic parameters are measured at different temperatures. By the Law of Approach to Saturation (LATS), the effective magnetic anisotropy constants K-E of granular gamma-Fe2O3 powders at different temperatures are obtained. By using the mixed-coercivity model, a good explanation is given to the temperature dependence of the coercivity for granular gamma-Fe2O3. It is found experimentally, for the first time, that the variation tendency of K-E with temperature for granular gamma-Fe2O3 is about the same as that of the shape magnetic anisotropy K-sh, and that the magnetization reversal process of granular gamma-Fe2O3 is close to uniform rotation at different temperatures.