Exploring the impact of thorium on the magnetic ordering of U4+ in a mixed oxide system

The various properties of uranium dioxide (UO2) have been researched extensively through its use as a nuclear fuel. In addition, due to the presence of strongly correlated 5f electrons UO2 has unique magnetic and electronic properties exhibiting a first-order antiferromagnetic (AFM) ordering, together with an ordering of the 5f electric quadrupoles, where TN = 30.8 K. Mixed actinide oxides comprised of (UxTh1-x)O2 provide an attractive alternative to UO2, also presenting several interesting research benefits, introducing the ability to change the exchange interactions between U 5f electrons as Th has no such electrons. Currently, there are several discrepancies in the critical paramagnetic composition (xc), the Th composition below which AFM ordering disappears. In this proposal, we consider the effect of Th content on the AFM ordering of UO2, by studying: (i) xc; (ii) the effect of Th on the internal distortion of the oxygen sublattice; (iii) changes to the U4+ electric quadrupoles.