Phase transitions in MnO and FeO at low temperatures: A neutron powder diffraction study

A powder neutron diffraction study of MnO and Fe0.92O was conducted at temperatures between 1.5 and 298 K in order to establish the relationship between magnetic and structural phase transformations. For MnO a strong coupling between magnetic ordering and cubic-to-rhombohedral transitions, as predicted by theory, could not be confirmed, neither rejected. For Fe0.92O a structural distortion was observed at a temperature of ∼50 K lower than the Néel transition, implying indirect relations between the two phenomena.