Crystallographic and magnetic properties of UAuSn

The uranium intermetallic compound UAuSn has been studied by means of neutron powder diffraction. It crystallizes in the ${\mathrm{CaIn}}_2$ structure type, with space group P$6_3$/mmc, in agreement with previous x-ray work. Below 37 K, it exhibits long-range antiferromagnetic order, in a double-sized orthohexagonal magnetic unit cell. At the lowest temperature measured, the uranium moment is 1.10${\mathrm{\mu }}_{\mathit{B}}$. The magnetic structure is collinear with moments parallel to the orthorhombic b axis and the magnetic space group is ${\mathit{C}}_{\mathit{p}}$m’cm’. We discuss the Au/Sn disorder in terms of metallic radii and discuss the consequences of this symmetry on the collinearity of the magnetic structure. These results are compared with work on the isostructural compounds UPdSn and UCuSn.