Magnetic properties of pentavalent uranium ternary oxides with fluorite structure Part II

BiUO4, MgU2O6 and SrU2O6 have been prepared and then identified by powder X-ray diffraction analysis. All the magnetic susceptibility vs. temperature curves have a peak at around 4-7 K with a similar shape. The effective number of Bohr magnetons is 1.46, 1.23 and 1. 29 and the temperature of Xmax is 4.4, 7.4 and 5 K for BiUO4, MgU2O6 and SrU2O6 respecitvely. These temperatures of Xmax fall in the same temperature range as for ScUO4, YUO4, CaU2O6 with the fluorite structure reported previously. The electron paramagnetic resonance parameters of g factor and linewidth for the present three mixed oxides are 2.3, 2.1 and 2.2 (which is slightly anisotropic) and 0.09, 0.069 and 0.03 T respectively. These g values are explained by crystal field theory for U5+ with [Rn]5f1 configuration in a crystal field with eightfold cubic symmetry. On the other hand, the magnetic susceptibility vs. temperature curves with the maximum are almost reproduced by scaling the curve obtained by calculation using an isotropic Heisenberg interaction model with S= 1/2 .