Superconducting properties in bulk nanostructured niobium prepared by high-pressure torsion

We have measured the magnetization M(T, H) and the resistivity rho(T) in bulk nanostructured Nb prepared by high-pressure torsion (HPT) and studied the effect of the grain refinement on the superconducting properties. With increasing revolution numbers N of HPT, the critical temperature T-c and the critical current density J(c) increase. The enhancement of T-c is consistent with the size effect for nanoscale superconductors. The increase of J(c) can be explained by the enhanced vortex pinning due to the introduction of lattice defects such as dislocations and grain boundaries. (C) 2013 Elsevier B.V. All rights reserved.