Effect of magnetic field cooling and magnetization anomaly in magnetic fluids near melting point

The magnetization process of ferrofluids with carrier fluids of water, paraffin, and alkylnaphtalene was investigated in a temperature range from 77 to 300 K as functions of the freezing rate and the intensity of cooling magnetic fields. A uniaxial magnetic anisotropy is induced by field cooling in frozen ferrofluids. This induced anisotropy which is caused by the formation of clustering of magnetic particles disappears on heating near the melting point. The magnetization of the frozen fluids exhibits an anomalous increase below the melting point of the carrier fluids. In a frozen state, no relative motion of particles, such as Brownian motion, occurs. With increasing temperature, the inhibited motion will be released gradually by the recovery of viscosity. The anomaly may be related to glassy transition and premelting. These magnetic properties are discussed in terms of mesoscopic phase transition between liquid and solid.