The Role of Stacking Faults in the Enhancement of the a-b Plane Peak in Silver Ion-Irradiated Commercial MOD REBCO Wires

The magnetic-field anisotropy of the critical current is an extrinsic property of superconducting wires that is of greatest relevance to the design of high temperature superconducting (HTS) devices. It is also a highly useful diagnostic tool to understand the dominant flux-pinning mechanisms active in different temperature and field regimes. REBa2Cu3O7 (REBCO) coated conductors typically exhibit a large peak in critical current when the field is aligned with the REBCO a-b plane. The commercial pinning-enhanced American Superconductor Corporation (AMSC) REBCO coil wire used for this study is unusual in having a relatively small a-b plane peak at higher temperatures due to an inherently low density of stacking faults. Stacking faults can then be introduced by annealing the wire in oxygen to create the more commonly observed strong a-b plane peak. Complementary c-axis columnar defects can be added by silver ion-irradiation producing an additional peak in the critical current at 0°. The resulting complex critical current anisotropy is studied using transport critical current measurements over a temperature range from 20 K to 77.5 K and under magnetic fields up to 7 T. Through systematic studies on pristine and annealed samples, in the presence and absence of columnar defects created by silver irradiation, we investigated the flux-pinning interactions between stacking faults and columnar defects.