Rare earth (RE – Ce, Gd) modified Nd1−xRExFeAsO0.7F0.3 superconductor with enhanced magneto-transport properties

Abstract

The influence of rare earth (RE – Ce, Gd) doping at the Nd site in the NdFeAsO_0.7F_0.3 superconductor wherein Ce and Gd have ionic radii in the order Ce > Nd > Gd is investigated. The structural and superconductivity characterization of the pure and doped samples show that Ce doping enhances the T_C of Nd_1−xRE_xFeAsO_0.7F_0.3 to a maximum of 53.6 K at x = 0.1 while Gd doping attains a T_C of 55.1 K at x = 0.15. Interestingly, both Ce and Gd doping create neither secondary phases nor precipitates within the detection limit of XRD. However, the lattice defects due to Ce and Gd doping modifies NdFeAsO_0.7F_0.3 and assists in pinning the flux lines on these defects thereby exhibiting an enhanced J_C(H) performance especially at high fields. It is also observed that the relatively small ionic size of Gd is more effective in T_C enhancement, while the lattice defects due to larger ionic size of Ce favor the remarkable enhancement of J_C(H).