Phase Transition of a Random Magnet, Ni_pMg_(1−p)(OH₂)

Abstract

The magnetic phase transition of the mixed crystals of nickel and magnesium hydroxides, Ni_pMg_(1−p)(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.