X-ray resonance exchange scattering in UAs.

Resonant enhancement of the magnetic x-ray scattering cross section in UAs has been investigated by tuning the incident x-ray energy through the uranium M/sub IV/ and M/sub V/ absorption edges. At the M/sub IV/ edge the intensity for the (0,0),(5/2) magnetic reflection is enhanced by 10/sup 7/ relative to the nonresonant component far above the edge, and is a remarkable 1% of the intensity of the (0,0,2) charge peak. At the M/sub V/ edge the enhancement is 10/sup 5/. The dramatic enhancement at M edges has been predicted by Hannon et al., and arises from strong electric multipole transitions between atomic core states and the exchange-split Fermi edge states.