Magnetoelastic Phase Transitions and Critical Behaviour of (Fe$\text{}_{1-x}$Ni$\text{}_{x}$)$\text{}_{2}$P System

This report focuses on magnetoelastic properties and critical behaviour of (Fe$\text{}_{1-x}$Ni$\text{}_{x}$)$\text{}_{2}$P system. For low Ni content (x=0.01) an isolated critical point was found. Analysis of this critical behaviour in the frame of molecular field approximation was carried out. Moreover, thermal variations of the lattice parameters, as measured by X-ray diffraction techniques, were studied. The (P,T) phase diagrams obtained for several Ni contents show the evidence that the Curie temperature decreases with pressure. The Mössbauer spectra collected for x = 0.025, 0.1, 0.2, 0.25 at different temperatures are also analysed. The existence of two nonequivalent crystallographic sites occupied by iron atoms as well as local magnetic structure is discussed.