THORIUM-DOPING INDUCED HIGH-Tc SUPERCONDUCTIVITY IN Dy1-xThxFeAsO

Parent compound of DyFeAsO was successfully synthesized by solid-state reaction under ambient pressure and superconductivity was induced by partial substitution of trivalent Dy3+ ions with tetravalent Th4+ in Dy1-xThxFeAsO. In the undoped parent compound, an anomaly in the resistivity appears around 140 K which corresponds to the structural phase transition and/or antiferromagnetic (AFM) order of the magnetic moments of Fe2+ ions. At low temperature, another AFM order associated with the magnetic moments of Dy3+ ions occurs at T-N of 9.55 K. The AFM order around 140 K has significant influence on the transport properties, which can be interpreted by opening of partial gap on Fermi surface. Th doping suppresses the AFM order related to the Fe2+ ions and the midpoint transition temperature T-c(mid) of 49.3 K is observed for x = 0.3. Our results also indicate that the [Ln(2)O(2)](2+) layer has influence on the magnetism of [Fe2As2](2)-layer.