The magnetic phase diagram and exchange parameters in NiCl ₂·2H₂O

Magnetization and susceptibility measurements on NiCl₂· 2H₂O have been performed for T=1-150 K. From the results it follows that NiCl₂·2H₂O orders antiferromagnetically at 7.2 K. The ordering consists of weakly coupled ferromagnetic chains. At T=6.3 K a zerofield reorientation of magnetic moments occurs which gives rise to a different kind of ordering. In the ordered state the magnetic phase diagram has been measured in three different directions in fields up to 120 kOe. From this complicated phase diagram, which at least can be qualitatively understood, fairly accurate estimates for the exchange constants and single ion anisotropy could be deduced.