Two dimensional antiferromagnetic ordering in MnPS3

Abstract

MnPS3 with space group C— has a layered monoclinic structure. Within the layers the manganese atoms form a hexagonal net with each manganese atom having three manganese neighbours within the layer. Below 80K the magnetic structure is three dimensional with the antiferromagnetic ordering within the layers coupled ferromagnetically between the layers and the moment direction perpendicular to the layers. We report the discovery of a truly two dimensional antiferromagnetic ordering in the temperature range 80-130K. This order is not immediately obvious from a neutron powder diffraction pattern as the antiferromagnetic intensity appears as rods rather than spots in reciprocal space and is therefore smeared out in a powder pattern. Preliminary analysis indicates that the moment in the two dimensional structure lies in the layer plane. If this is so it would have to result from a unidirectional rather than planar anisotropy so that the system is described within the Ising model, the only model which will sustain long range magnetic order in two dimensions. The neutron diffraction data at various temperatures will be presented along with supporting single crystal susceptibility measurements.