Effects of Mn and Ni doping on the superconductivity of SmFeAs(O,F)

Abstract We have studied the effects of 3 d metal Manganese (Mn) and Nickel (Ni) doping on the superconducting properties of SmFeAs(O,F) bulk samples, synthesized through low temperature synthesis route. Ni-doping depresses the superconductivity but the resistivity becomes still metallic nature. These observations indicate that Ni works as electron donors. In contrast, Mn-doping suppresses the superconductivity faster than the Ni and led to enhanced resistivity especially in the low temperature region, suggesting that Mn ions act as scattering centers. The effects of the transition metal doping in conducting layer (FeAs) has been discussed by the variation of the lattice parameters and resistivity with doping. The temperature dependence of resistivity under external magnetic field has been studied and indicates that the slope of the upper critical field ( μ 0 d H c 2 /d T ) is slightly improved by Mn doping and reached up to −9.5 T K −1 . The normal state thermoelectric power ( S ) decreases rapidly with Mn and Ni doping, and shows the negative value in the whole temperature region for all samples, suggesting that an electron-type charge carrier dominates in the transport properties.