Chemical and magnetic ordering in Fe0.5Ni0.5 PS 3

Abstract

The MPS 3 family of layered magnetic materials (M = Fe 2+ , Ni 2+ , Mn 2+ , etc) shows many unusual properties. We have recently observed time-dependent magnetisation and two magnetic phase transitions in Fe 0.5 Ni 0.5 PS 3 , 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 Ni 2+ . 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 (Fe 3 , Fe 2 Ni, FeNi 2 and Ni 3 ) are possible may indicate that the mixture is not random, but shows some local ordering; the neutron results show evidence for a similar conclusion.