Large pinning forces and matching effects in YBa₂Cu₃O_7-δ thin films with Ba₂Y(Nb/Ta)O₆ nanoprecipitates

The addition of mixed double perovskite Ba₂Y(Nb/Ta)O₆ (BYNTO) to YBa₂Cu₃O_7−δ (YBCO) thin films leads to a large improvement of the in-field current carrying capability. For low deposition rates, BYNTO grows as well-oriented, densely distributed nanocolumns. We achieved a pinning force density of 25 GN/m³ at 77 K at a matching field of 2.3 T, which is among the highest values reported for YBCO. The anisotropy of the critical current density shows a complex behavior whereby additional maxima are developed at field dependent angles. This is caused by a matching effect of the magnetic fields c-axis component. The exponent N of the current-voltage characteristics (inversely proportional to the creep rate S) allows the depinning mechanism to be determined. It changes from a double-kink excitation below the matching field to pinning-potential-determined creep above it.