URANIUM 5F SHELL IN UPD2AL3 AND URU2SI2 STUDIED BY X-RAY MAGNETIC CIRCULAR-DICHROISM

We report x-ray magnetic circular dichroism (XMCD) measurements perfor med at the uranium M-4,M-5 edges in the paramagnetic phase of the heav y fermion superconductors UPd2Al3 and URu2Si2. The analysis of the spe ctra with the first sum rule yields the orbital moment of the 5f shell for both compounds. The shape of the dichroic spectrum at the M-5 edg e for the two compounds is qualitatively different: a single lobe is o bserved for URu2Si2 and two lobes are detected for UPd2Al3. This two l obe structure reflects the strong effect of the interaction of the ura nium 5f electrons with their environment in the latter compound.