抄録
Magnetization in metamagnetic FeCl2·2H2O has been studied in detail under both a pulsed and a static magnetic fields at temperatures between 1.5 K∼14 K. At high temperatures, a transition from the antiferromagnetic (A.F.) to the ferromagnetic (Ms⁄3) states at Hc1 and that from the Ms⁄3 to the ferrimagnetic (Ms) states at Hc2 are observed. A large hysteresis has been observed at Hc1 even under a slowly varying field. As the temperature is lowered, a transition from the A.F. to a Ms⁄2 states followed by that from the Ms⁄2 to the Ms⁄3 states accompanying with that from the Ms⁄3 to the Ms states takes place in an increasing field. The Ms⁄2 state which is a high energy state in this salt becomes stable with decreasing temperature. Below 2.24 K, a large hysteresis at Hc2 is observed even under a slowly varying field.
It is shown that the main origin of the anomalously large hysteresis comes from the energetic barrier due to a strong single ion anisotropy energy. The appearance of a new phase (Ms⁄2 state) arises from the fact that a Ms⁄2 state is constructed by a simple reversal of down spins in the A.F. state, while the Ms⁄3 state by a complicated rearrangement of up and down spins.
