CRYSTAL-STRUCTURE, MAGNETIC AND ELECTRICAL-TRANSPORT STUDIES OF SINGLE-CRYSTALS OF THE URANIUM MIXED CHALCOGENIDES - USSE, USTE AND USETE

The crystal structure of USSe, USTe and USeTe was refined from single crystal X-ray diffraction data. All these uranium mixed chalcogenides crystallize in the orthorhombic unit-cell related to the PbCl2 type. M agnetic studies on single crystals have confirmed their ferromagnetic behaviour with the Curie temperatures of 24, 85 and 69 K respectively. The saturation and effective moments per uranium atom are similar to 1.5, 1.55, 1.62(mu B), and 3.16, 2.92, 3.04(mu B), respectively. The e lectrical resistivity measured between 4.2 and 300 K indicated a pseud o-semimetallic behaviour for USTe and USeTe, while for USSe this is ob served only above T = 50 K. Below this temperature, a more complex res istivity behaviour observed for this compound [maximum and minimum in rho(T)] probably indicates its semiconducting properties with an energ y gap of 470 K above T-C, which is gradually closed in the magneticall y ordered region with lowering of the temperature.