Evaluation of remanent field distributions on Bi2223 tapes with oxide barriers by using scanning Hall-probe microscopy

Abstract

Introducing oxide barriers around the superconductor filaments is an effective way to increase the matrix resistivity for AC loss reduction in Bi2223 tapes. However, because of the poor ductility of barrier oxides, the uniformity of the transport property along a tape length could be easily deteriorated. To qualify the uniformity along a length of barrier tape, therefore, simple and non-destructive evaluation techniques should be urgently required. In this study, we measured the remanent field distributions on the surface of Bi2223 tapes with Ca2CuO3 barriers by using scanning Hall-probe microscopy (SHM). By moving the permanent magnet on the tape surface along a length direction, an external field in perpendicular to the broader face of a tape was applied at 77 K. After removing the field, the distributions of remanent field Brz in perpendicular to a tape surface were measured by SHM. The results indicated that the Brz at a fixed distance of 0.5 mm away from a tape surface shows the maximum near the centre of transverse tape section, but the magnitude and uniformity of the maximum Brz was degraded significantly by introducing barriers. We also confirmed that there were strong correlation between the distributions of the maximum remanent field and the transport critical current Ic along a tape length. This indicates that the longitudinal uniformity of transport property for a barrier tape could be investigated simply and non-destructively by SHM.