Eur. Phys. J. B 79, 139-146 (2011)
https://doi.org/10.1140/epjb/e2010-10674-x

Physical property characterization of single step synthesized NdFeAsO_0.80F_0.20 bulk 50 K superconductor

¹ National Physical Laboratory (CSIR), Dr. K.S. Krishnan Marg, 110012 New Delhi, India
² Department of Physics, University of Rajasthan, 302055, Jaipur, Rajasthan, India

Corresponding author: ^a awana@mail.nplindia.ernet.in

Received: 2 September 2010
Revised: 10 November 2010
Published online: 21 December 2010

Abstract

We report an easy single step synthesis route of title compound NdFeAsO_0.80F_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_0.80F_0.20 superconductor. The granularity of the bulk superconducting NdFeAsO_0.8F_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.