Irreversible behaviour of oriented grained YBa 2Cu 3O x. Part 1: transport and shielding currents

Abstract

The critical current of oriented grained YBa 2Cu 3O x bulk material was investigated by resistive transport and inductive flux profile measurements. The applied magnetic field was directed parallel and perpendicular to the a–b plane. No features of granularity could be detected if the induced shielding current directed along the c-axis passed grain boundaries. The comparison of shielding and transport currents further ruled out the existence of intragrain junctions. The observation of a temperature scaling law for the volume pinning force allows comparison of the pinning strengths in both geometries. The volume pinning force is found to be about one order of magnitude larger if the magnetic field is parallel to the twin planes. Its field dependence resembles grain boundary pinning due to electron scattering, as observed in Nb 3Sn. In the perpendicular geometry pinning may be explained by a collective interaction due to intrinsic or background pinning. The flux bundle volume, which may be identified with the correlation volume of the collective model, was experimentally determined.