INFLUENCE OF CRYSTALLITE SIZE AND SHAPE ON THE VISCOUS MAGNETIZATION OF GAMMA-FE2O3 PARTICLES

The usefulness of the normalized thermal fluctuation field in magnetic granulometry is confirmed with data for gamma-Fe2O3 and CrO2. The variation of the normalized fluctuation field with crystallite diameter in the gamma-Fe2O3 follows a similar trend for both isometric and longitudinal crystallite growth even though in the second case the diameter is not a good guide to the volume of the crystallites. This suggests that the smallest dimension of the crystallite rather than its volume is critical for the activation volume; after correction for the differences in coercivity a long, thin particle is more subject to thermal activation than a short, thick one of the same volume.