Antiferromagnetism in MUO3 (M=Na,K,Rb) studied by neutron diffraction

Simultaneous refinements of X-ray and neutron powder diffraction patterns taken on the M UO 3 perovskite compounds with M =Na, K and Rb, were performed to reveal anisotropy in the temperature factors, mainly of oxygen. No anisotropic thermal motion was found. The magnetic ordering of the compounds has been investigated with low temperature neutron diffraction. It is found that all these compounds show G-type antiferromagnetic ordering with a similar, orthorhombic magnetic unit cell. The propagation vector could only be determined for the orthorombic NaUO 3 compound and was found to point in the z -direction. The refined magnetic moment for U 5+ in these structures was found to be around 0.20(3) μ B .