Granularity-induced field-hysteresis of transport critical current in patterned coated conductors*

In superconducting coated conductors such as RABiTS and IBAD films, intergranular misorientations have been effectively minimized, but a small number of local, higher-angle misorientations remain. One important effect of such weak links is the hysteresis of the critical current density $J_{c}$ with respect to applied field $H$, brought about when large circulating currents trapped within adjacent grains produce a focused field within the grain \textit{boundaries }(GB's) which can partially cancel out $H$ when applied field is \textit{decreasing}, thus shifting the maximum $J_{c}$ from zero $H $to a finite field where the local field at the GB is at minimum. This effect has been seen recently in measurements of magnetization (\textit{induced}) currents, but has not been documented using transport (\textit{applied}) current. However, in samples that are \textit{patterned} into conduits 200 $\mu $m wide or less, the hysteretic effect on transport $J_{c}$ is clearly seen. This discrepancy between `magnetization $J_{c}$' and `transport $J_{c}$' may be due to differences in voltage criterion between the two types of measurement, as will be discussed. Systematic measurements and analyses will be presented, along with ramifications for applications.