Transport $J_{{c}}$ 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.