Transport J} in Bulk Superconductors: A Practical Approach?

The characterization of the critical current density of bulk high-temperature superconductors is typically performed using magnetometry, which involves numerous assumptions, including, significantly, that J c within the sample is uniform. Unfortunately, magnetometry is particularly challenging to apply where a local measurement of J c across a feature, such as a grain boundary, is desired. Although transport measurements appear to be an attractive alternative to magnetization, it is extremely challenging to reduce the cross-sectional area of a bulk sample sufficiently to achieve a sufficiently low critical current that can be generated by a practical current source. In the work described here, we present a technique that enables transport measurements to be performed on sections of bulk superconductors. Metallographic techniques and resin reinforcement were used to create an I-shaped sample of bulk superconductor from a section of Gd-Ba-Cu-O containing 15 wt % Ag 2 O. The resulting superconducting track had a cross-sectional area of 0.44 mm 2 . The sample was found to support a critical current of 110 A using a field criterion in the narrowed track region of 1 μV cm -1 . We conclude, therefore, that it is possible to measure critical current densities in excess of 2.5 × 10 8 A m -2 in sections of a bulk superconductor.