Neodymium-Doping Induced Superconductivity in 1111-SrFeAsF Iron-Pnictide System

Polycrystalline Sr1−xNdxFeAsF samples at various Nd-doping levels have been prepared by conventional solid-state synthesis close to ambient pressure. Susceptibility and resistivity were studied down to 4 K showing superconductivity competing with a low-temperature magnetic ordering and probably the coexistence of both, well into the superconducting region. The temperature dependence of the resistivity of all the Nd-doped samples clearly show the presence of this transition below 15 K, most likely originating from the magnetic ordering of Nd moments. This transition is gradually attenuated but not completely suppressed even at optimum-doping region at x≈0.54. The spin-density wave anomaly at 175 K survives up to 0.35 Nd-doping, while superconductivity occurs only above x=0.40. The maximum onset transition temperature, Tc, reaches as high as 54.3 K for x=0.70, but superconductivity disappears beyond that. The estimated upper critical fields, Hc2, are high, with values exceeding 98 Tesla obtained from two samples of different doping level.