Phase Transition of a Random Magnet, NipMg(1-p)(OH2)

The magnetic phase transition of the mixed crystals of nickel and magnesium hydroxides, Ni p Mg (1- x ) (OH) 2 , as randomly diluted magnets was investigated by measurements of the susceptibilities. The critical curve (phase transition temperatures versus concentrations, p ) shows a terraced form in the concentration region below p ∼ 0.4, which might reflect the quasi-two dimensionality of Ni(OH) 2 . The critical concentration, p c , is estimated as about 0.1. Furthermore, the dilution of Ni(OH) 2 by Mg(OH) 2 changes the values of θ/ T ° max and χ M ° ( T =0)/χ M ° max , and the shape of the peak of the susceptibility, where T ° max is the temperature at which the susceptibility, χ M ° , has a peak value, χ M ° max . These changes are interpreted as a result of the change of the spin arrangement in an ordered state depending on the concentration, p .