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, U2N3, 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 TN is not observed. Instead, we propose that the strong magnetoelastic interaction below
TN 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 α−U2N3, no single crystals have been previously prepared, and we have determined the AF ordering wave vector. The AF TN is close to that previously reported. In addition, resonant diffraction methods have identified an aspherical quadrupolar charge contribution in U2N3 involving the 5f electrons.