Spectral Line Shapes of U M2- and As K-edge Resonant X-ray Scattering in the Two Antiferromagnetic Phases of UAs

We present resonant x-ray scattering measurements on uranium arsenide at the U M2 and As K absorption edges. The studies at both edges relate to aspects of the hybridization involving the 5f states in UAs. At the U M2 edge, the spectral line shapes are found to differ between the two antiferromagnetic phases of UAs. In the type-I phase, the line shapes may be fitted using a single resonant component, whereas in the type-IA phase, a second resonant component, 3.5 eV above the first component, is required to fit the line shapes in the rotated polarization scattering channel. The possibility that the single first component in the type-I type-IA phase corresponds to E2 scattering due to the ordered 5f magnetic-dipole moments and that in the type-IA phase the second component represents an E1 process involving polarized 6d U states is considered. Similar line shapes are observed for the two antiferromagnetic phases at the As K edge, a result which is in discordance with a recent theoretical prediction. The experimentally observed As K-edge line shape has an asymmetrical form in both phases, which possibly relates to As 4p-band effects unaccounted for in the theory.JRC.E.6-Actinides researc