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.

Zero-field-cooled (ZFC) magnetization, field-cooled (FC) magnetization, AC magnetic susceptibility and major hysteresis loops of sintered SrRuO3 have been measured over the range of magnetic ordering temperature. The data were analyzed within the framework of the Preisach model. The numerical simulations match the major features of ZFC/FC magnetization. The results indicate that various ZFC/FC behaviors originate from the applied field and the Barkhausen spectrum of the sample.

A series of n-type Zn1-xCuxO (x = 0.02, 0.06, 0.10, and 0.12) films was prepared using direct current reactive magnetron sputtering. Magnetic measurements indicate that all the films are ferromagnetic at room temperature and the moment per Cu ion decreases with increasing copper concentration and nitrogen doping. The observed magnetic moment was 1.8

Ionic size is considered to be an important factor influencing the unit cell volume of manganites with an ABO3 structure. For La1-xSrxMnO3, however, although the average effective ion radius of all cations taken together increases with increasing x, the unit cell volume decreases for x<0.5. In the case of La1-xNaxMnO3, the unit cell volume reaches a minimum when x = 0.3. Up to now, no satisfactory explanation of these phenomena has been found. In this letter, an explanation based on the ionic cohesive energy with a small additional metallic cohesive energy is described.

From the measurements of the ac susceptibility of SrRuO3, we determine the critical temperature TC=159.7 ± 0.2 K and critical exponents δ = 2.50 ± 0.15 (from the critical isotherm orδ= 3.17 ± 0.20 (from magnetization versus magnetic field at Curie temperature), γ+β = 1.50±0.05 (from the temperature dependence of the internal field of the crossover line), and γ = 0.96 ± 0.05 (from the temperature dependence of the susceptibility along the same line). These exponent values are very close to those predicted by the mean field model.