Anisotropic magnetic-field hysteresis behaviors in 7-filamentary Cu/Ag-sheathed Ba1−xKxFe2As2 tapes

We investigated the magnetic-field dependence of the critical current (Ic) in seven-filament copper/silver composite-sheathed Ba1−xKxFe2As2 (Ba122) tapes. A magnetic hysteresis was observed when the external magnetic field (B) was increased and decreased, depending on its orientation relative to the tape. Ic exhibited a non-monotonic dependence on the magnetic field as B increased. In terms of angular dependence, a more pronounced magnetic hysteresis and a significant upturn in Ic with increasing B were observed at 90° (B//tape) compared to 0° (B⊥tape). These angular-dependent hysteresis and upturn behaviors were analyzed using a model that accounts for two current paths in the polycrystalline superconducting cores. The current transport occurs through in-plane and out-of-plane paths, differentiated by weakly linked vertical and horizontal grain boundaries. The magnetic field exerts distinct effects on these grain boundaries, influencing the current flow in each path and resulting in the anisotropic behavior of Ic. Targeted modifications to the vertical and horizontal grain boundaries could potentially enhance Ic and better control anisotropy.