Crystal structure and magnetic properties of the hexagonal uranium dichalcogenides γUS2 and γUSe2

The crystal structure of the hexagonal uranium disulfide γUS2 (hexagonal P62m, a = 7.236(2) Å, c = 4.062(1) Å, γ = 120 °) has been determined from single crystal X-ray diffraction data and confirmed by Rietveld refinements from X-ray powder diffraction intensities of the isostructural selenide γUSe2 (a = 7.6328(3) Å, c = 4.1897(2) Å, γ = 120 °). They crystallize with the antiFe2P-type structure. The sulfide γUS2 exhibits weak ferromagnetism below ≈10 K, and the selenide is a ferromagnet with a Curie temperature of ≈20 K and an ordered moment of 0.72 μB/U under 20 kGauss.