凍結磁性流体の磁気異方性

抄録

The magnetization process of a ferrofluid whose carrier fluid is paraffin was investigated in a temperature range from 77K to 300K as a function of the intensity of cooling field and the freezing rate. Phase transition between liquid state and solid state can be simulated by using the ferrofluids as a magnetic probe. The uniaxial magnetic anisotropy was induced by field cooling in frozen ferrofluids. This induced anisotropy decreased with increasing temperature near the melting point and disappeared at 30K higher temperature than the melting point. In this region the rotational hysteresis was observed. The anisotropy constant K near the melting point was described by the equation K=A·exp(ΔE_K/kT). The value of the activation energy ΔE_K was almost the same as that of ΔE_η estimated from the viscosity vs. temperature relation η∝ exp(ΔE_η/kT).