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 X_max is 4.4, 7.4 and 5 K for BiUO₄, MgU₂O₆ and SrU₂O₆ respectively. These temperatures of X_max fall in the same temperature range as for ScUO₄, YUO₄, CaU₂O₆ and CdU₂O₆ 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.