Weak ferrimagnetism, compensation point, and magnetization reversal in Ni(HCOO)2•2H2O -: art. no. 224422

The nickel (II) formate dihydrate Ni(HCOO)(2).2H(2)O shows a peculiar magnetic response at T<T-N=15.5 K. The magnitude of the weak magnetic moment increases initially below T-N, is zero at T-*=8.5 K, and increases again at lowered temperature. The sign of low-field magnetization at any given temperature is determined by the sample's magnetic prehistory and the signs are opposite from each other at T<T-* and T-*<T<T-N. This behavior suggests that Ni(HCOO)(2).2H(2)O is a weak ferrimagnet and T-* is a compensation point. The magnetic properties of Ni(HCOO)(2).2H(2)O can be understood by taking into account the features of its crystal structure. There are two nonequivalent Ni sites in the monoclinic P2(1)/c structure of this compound, forming two magnetic subsystems. Each of these subsystems is weakly ferromagnetic due to the canting of predominantly antiferromagnetic sublattices. The weak ferromagnetic moments of these subsystems are oriented opposite from each other, resulting in weak ferrimagnetism. The model proposed explains the main features of the experimentally observed phenomena.