Physical property characterization of single step synthesized NdFeAsO 0.80 F 0.20 bulk 50 K superconductor

We report an easy single step synthesis route of title compound NdFeAsO 0.80 F 0.20 superconductor having bulk superconductivity below 50 K. The title compound is synthesized via solid-state reaction route by encapsulation in an evacuated (10 -3 Torr) quartz tube. Rietveld analysis of powder X-ray diffraction data shows that compound crystallized in tetragonal structure with space group P4/nmm. R(T)H measurements showed superconductivity with T c (R=0) at 48 K and a very high upper critical field (H c2 ) of up to 345 T. Magnetic measurements exhibited bulk superconductivity in terms of diamagnetic onset below 50 K. The lower critical field (H c1 ) is around 1000 Oe at 5 K. In normal state i.e., above 60 K, the compound exhibited purely paramagnetic behavior and thus ruling out the presence of any ordered FeO x impurity in the matrix. In specific heat measurements a jump is observed in the vicinity of superconducting transition (T c ) along with an upturn at below T=4 K due to the AFM ordering of Nd +3 ions in the system. The Thermo-electric power (TEP) is negative down to T c , thus indicating dominant carriers to be of n-type in NdFeAsO 0.80 F 0.20 superconductor. The granularity of the bulk superconducting NdFeAsO 0.8 F 0.2 sample is investigated and the intra and inter grain contributions have been individuated by looking at various amplitude and frequencies of the applied AC drive magnetic field. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2011