Neutron diffraction determination of the magnetic phases of CoCl2·2H2O

The metamagnetic behaviour of CoCl₂·2H₂O has been determined by means of neutron diffraction. At T = 4.2 K the reflections of the antiferromagnetic zero-field phase disappear, when a magnetic field of H_c1 = 31.8 kOe is applied along the b axis. The new ferrimagnetic phase vanishes at H_c2 = 46.1 kOe and the magnetically saturated configuration is reached. The three phases meet at a triple point at T_T = 8.9 K and H_T = 37.5 kOe. Two types of phase transition have been detected.