Effect of Y Doping on Superconductivity and Spin-Density-Wave States in Sm1−xYxFeAsO0.8F0.2 and Sm1−xYxFeAsO

Y doping effects on crystal structure, resistivity, superconductivity, and spin-density-wave states in the parent and F-doped SmFeAsO compounds have been studied. Y doping leads to shrinkage of the lattice parameters in both systems. The superconductivity of Sm1−xYxFeAsO0.8F0.2 is suppressed by Y doping with onset Tc decreasing monotonically from 52.6 K at x=0 to 25 K at x=0.5. A weak resistivity anomalies around 120 K ascribed to the spin-density-wave instability is observed in the sample of x=0.5. In parent SmFeAsO compound, the resistivity anomaly temperature was detected to be around 150 K and shifted towards lower temperatures with the Y doping level increased. It is concluded that a negative pressure effect takes responsibilities for the decrease of Tc in Sm1−xYxFeAsO0.8F0.2.