Itinerant ferromagnetic SrRuO3 with a Curie temperature TC 160.7 K was prepared by a conventional solid reaction method. Its zero-field-cooled (ZFC) magnetization and field-cooled (FC) magnetization were measured over a temperature interval from 5–180 K, in a sequence of applied fields up to coercivity. The major hysteresis loops were measured over a range of temperatures, which span the ordered phase. An empirical model was proposed to analyze the ZFC behaviors by means of coercivities at different temperatures. The calculated ZFC magnetization is consistent with the measured ZFC magnetization. Different ZFC magnetization behaviors were explained by using this model. The results indicate that the various ZFC behaviors originate from the comparison between the temperature dependence of FC magnetization and that of coercivity.

Zero-field-cooled (ZFC) magnetization, field-cooled (FC) magnetization, ac magnetic susceptibility and major hysteresis loops of itinerant ferromagnet SrRuO3 have been measured at magnetic ordering temperatures ranging from 5 to 160 K. An empirical model is proposed to calculate the measured ZFC magnetization. The result indicates that the calculated ZFC magnetization compares well with the measured one. Based on the generalized Preisach model, both the ZFC and FC curves are reproduced by numerical simulations. The critical temperature and critical exponents are determined by measuring the ac magnetic susceptibility in different bias magnetic fields at temperatures in the vicinity of the point of phase transition.

Zero-field-cooled (ZFC) magnetization, field-cooled (FC) magnetization and coercive fields of Sr1-x Cax RuO3, with x = 0.0, 0.2, 0.4 and 0.6, have been measured over the magnetic ordering temperature, in a sequence of applied fields. An empirical model has been proposed to analyze ZFC behaviors. The calculated ZFC magnetization is in agreement with the measured one. Different ZFC behaviors have been explained by means of the empirical model.

Granular γ-Fe2O3 powders, acicular γ-Fe2O3, and CoFe–γ-Fe2O3 powders are prepared by different methods. Particle shapes and mean particle sizes of samples are determined by transmission electron microscopy (TEM). Magnetic parameters are measured by a vibrating sample magnetometer (VSM) at different temperatures. Effective magnetic anisotropy constants K E of granular γ-Fe2O3 powders at different temperatures are obtained by using the law of approach to saturation (LATS). KE values of acicular γ-Fe2O3 and CoFe–γ-Fe2O3 powders are measured by a magnetotorquemeter. It is found for the first time that the variation tendency of KE with temperature for granular γ-Fe2O3 is about the same as that of shape magnetic anisotropy Ksh. Fluctuation field Hf and activation volume Vf of samples are measured. A theoretical expression of Vf is derived. For granular γ-Fe2O3 powders, calculated activation volumes are consistent with experimental ones at different temperatures. But as for acicular γ-Fe2O3 powders, calculated activation volumes are larger than experimental ones. Experimental results show that magnetization reversal of granular γ-Fe2O3 at different temperatures is close to homogeneous rotation.

The granular γ-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 KE of granular γ-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 γ-Fe2O3. It is found experimentally, for the first time, that the variation tendency of KE with temperature for granular γ-Fe2O3 is about the same as that of the shape magnetic anisotropy Ksh, and that the magnetization reversal process of granular γ-Fe2O3 is close to uniform rotation at different temperatures.