Structures and Magnetic Properties of New Inserted Uranium Tellurides: U3Te5Zx T (Z=Ge, Sn)

The two new compounds U3Te5Ge0.7 and U3Te5Sn0.5 were prepared by heating the binary compound U3Te5 and the corresponding group 14 element at 850°C in a fused-silica tube. Single crystals have been grown by chemical vapor transport using iodine as transporting agent in temperature gradients of 870-840°C and 840-800°C for U3Te5Ge0.7 and U3Te5Sn0.5, respectively. They have been characterized by single-crystal Xray diffraction measurements and by energy dispersive X-ray analysis. The two isostructural compounds crystallize with two formula units in the orthorhombic space group Pmmn in cells of dimensions: U3Te5Ge0.7a=4.2764(1) ?, b=13.1029(3) ?, c=8.9104(2) ?; U3Te5Sn0.5, a=4.3160(1) ?, b=13.1999(4) ?, c=8.9128(2) ?. The crystal structures comprise two independent U atoms with two different coordination geometries. Atom U(1) is surrounded by eight Te atoms in a bicapped trigonal prismatic geometry. Atom U(2) is in a seven coordinate environment of Te atoms, with an arrangement usually described as a 7-octahedron. The three-dimensional packing results in distorted hexagonal cavities where the metalloid atoms are inserted. Magnetic measurements reveal that both compounds U3Te5Ge0.7 and U3Te5Sn0.5 are hard ferromagnets with ordering temperature of 135 and 140 K, respectively. At low temperature, they display large magnetocrystalline anisotropy with origin on the domain wall pinning at the magnetic domain boundaries.