Magnetic Properties of Magnetic Fluids near Melting Point

The magnetization (M), field-induced magnetic anisotropy (Ku), rotational hysteresis loss (Erot) and melting point (Tm) of water-and paraffin-base ferrofluids were investigated in the temperature range from 77 K~300°K, as functions of the density of the colloidal particles. Both paraffin and paraffin-base fluids were melted down at temperatures between 180 and 210°K. In this range, the values of M and Erot for paraffin-base fluids increased, and the Ku decreased, with increasing temperature. These properties may be explained by assuming that liquid-state and solid-state regions exist in the paraffin in this temperature range, and that the volume of the solid-state region decreased with increasing temperature. Depression of the freezing point was observed in water-base fluids.