CRYSTALLOGRAPHIC AND MAGNETIC-PROPERTIES OF UPDSN

A single crystal of the intermetallic compound UPdSn has been studied by means of neutron diffraction using the white-beam Laue diffractometer (single-crystal diffractometer) at the Los Alamos spallation neutron source. Data were taken in the paramagnetic phase at 55 K and just below the Neel point at 37 K. The crystallographic data refine well within the space group P6(3)mc and confirm the results obtained previously on powders, namely that the Pd and Sn atoms are ordered. At low temperature, UPdSn undergoes two phase transitions at 40 and 25 K to complicated noncollinear antiferromagnetic structures. All three pairs of magnetic domains are observed, in roughly equal populations, in the intermediate-temperature orthorhombic magnetic structure (phase I). A uranium moment of 0.863mu(B) and canting angles phi=56.51-degrees and theta=21.42-degrees were obtained, in reasonable agreement with previous powder neutron data for this temperature. The observed form factor yields an orbital-to-spin moment ratio -mu(L)/mu(S)=2.6 which is characteristic of the trivalent f3 configuration.