Chemical and magnetic ordering in Fe 0.5 Ni 0.5 PS 3

Abstract

The MPS3 family of layered magnetic materials (M = Fe2+, Ni2+, Mn2+, etc) shows many unusual properties. We have recently observed time-dependent magnetisation and two magnetic phase transitions in Fe0.5Ni0.5PS3, and here we use neutron diffraction and Mössbauer spectroscopy to explore the magnetic and structural ordering. Neutron diffraction shows that the staggered magnetisation lies closest to the Brillouin curve for J = 1, which is the spin for quenched Ni2+. In agreement with neutron diffraction, Mössbauer spectroscopy shows a magnetic ordering temperature of ∼120K. It does not show any evidence of a second, low temperature (re)ordering, suggesting that the low temperature transition seen previously is a result of the time dependence of the magnetisation and is not apparent when the sample is given time to relax between measurements. The presence of three magnetic Fe-site environments when four chemical environments (Fe3, Fe2Ni, FeNi2 and Ni3) are possible may indicate that the mixture is not random, but shows some local ordering; the neutron results show evidence for a similar conclusion.