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 diffractomet er (single-crystal diffractometer) at the Los Alamos spallation neutro n source. Data were taken in the paramagnetic phase at 55 K and just b elow the Neel point at 37 K. The crystallographic data refine well wit hin the space group P6(3)mc and confirm the results obtained previousl y on powders, namely that the Pd and Sn atoms are ordered. At low temp erature, UPdSn undergoes two phase transitions at 40 and 25 K to compl icated noncollinear antiferromagnetic structures. All three pairs of m agnetic domains are observed, in roughly equal populations, in the int ermediate-temperature orthorhombic magnetic structure (phase I). A ura nium moment of 0.863mu(B) and canting angles phi=56.51-degrees and the ta=21.42-degrees were obtained, in reasonable agreement with previous powder neutron data for this temperature. The observed form factor yie lds an orbital-to-spin moment ratio -mu(L)/mu(S)=2.6 which is characte ristic of the trivalent f3 configuration.