Polarized neutron scattering and x-ray magnetic circular dichroism studiesof the heavy-fermion superconductor UNi2Al3

A polarized neutron scattering experiment and an x-ray magnetic circular di chroism (XMCD) study at the M-4,M-5 edges of uranium have been performed on a single crystal of the heavy-fermion superconductor UNi2Al3 in the parama gnetic phase. Projections of the maximum-entropy reconstructions of the mag netization distribution obtained from neutron data evidence a large and alm ost spherical distribution on the U sites and an induced moment at the Ni s ites. Refinements of the magnetic structure factors within the dipolar appr oximation allow one to quantify the Ni contribution and the orbital and spi n uranium moments, and reveal a diffuse contribution parallel to the 5f mom ent. The XMCD study leads to a value of the 5f orbital contribution in agre ement with the neutron one. For both neutron and XMCD experiments, we compa re our results with previous measurements performed on the parent compound UPd2Al3.