Synthesis, structure, and magnetic characterization of Cr₄US₈

The compound Cr₄US₈ has been synthesized at 1073 K and its crystal structure has been determined at 100 K. The structure is modulated with a two-fold commensurate supercell. The subcell may be indexed in an orthorhombic cell but weak supercell reflections lead to the monoclinic superspace group P2₁/c(α0γ)0s with two Cr sites, one U site, and four S sites. The structure comprises a three-dimensional framework of CrS₆ octahedra with channels that are partially occupied by U atoms. Each U atom in these channels is coordinated by eight S atoms in a bicapped trigonal-prismatic arrangement. The magnetic behavior of Cr₄US₈ is complex. At temperatures above ~120 K at all measured fields, there is little difference between field-cooled and zero field-cooled data and χ(T) decreases monotonously with temperature, which is reminiscent of the Curie-Weiss law. At lower temperatures, the temperature dependence of χ(T) is complex and strongly dependent on the magnetic field strength.