Synchrotron x-ray scattering of magnetic and electronic structure of UN and U2N3 epitaxial films

We examine the magnetic ordering of UN and of a closely related nitride, ${\mathrm{U}}₂{\mathrm{N}}₃$, by preparing thin epitaxial films and using synchrotron x-ray techniques. The magnetic configuration and subsequent coupling to the lattice are key features of the electronic structure. The well-known antiferromagnetic (AF) ordering of UN is confirmed, but the expected accompanying distortion at ${\mathrm{T}}_N$ is not observed. Instead, we propose that the strong magnetoelastic interaction below ${\mathrm{T}}_N$ causes substantial changes in the strain in the sample being measured. These strains vary as a function of the sample form. As a consequence, the accepted AF configuration of UN may be incorrect. In the case of cubic $\ensuremath{\alpha}\ensuremath{-}{\mathrm{U}}₂{\mathrm{N}}₃$, no single crystals have been previously prepared, and we have determined the AF ordering wave vector. The AF ${\mathrm{T}}_N$ is close to that previously reported. In addition, resonant diffraction methods have identified an aspherical quadrupolar charge contribution in ${\mathrm{U}}₂{\mathrm{N}}₃$ involving the $5f$ electrons.