Crystal structure and magnetic properties of the hexagonal uranium dichalcogenides gamma US2 and gamma USe2

The crystal structure of the hexagonal uranium disulfide gamma US2 (hexagonal P (6) over bar 2m, a = 7.236(2) Angstrom, c = 4.062(1) Angstrom, gamma = 120 degrees) has been determined from single crystal X-ray diffraction data and confirmed by Rietveld refinements X-ray powder diffraction intensities of the isostructural selenide gamma USe2 (a = 7.6328(3) Angstrom, c = 4.1897(2) Angstrom, gamma = 120 degrees). They crystallize with the anti-Fe2P-type structure. The sulfide gamma US2 exhibits weak ferromagnetism below approximate to 10 K, and the selenide is a ferromagnet with a Curie temperature of approximate to 20 K and an ordered moment of 0.72 mu B/U under 20 kGauss.