Dependence of transport critical current of magnetic field processedBi2Sr2CaCu2O8/AgMg tapes on the background magnetic field and magnetic field direction

Abstract

The background magnetic field dependence of the critical current(Ic) is studied on magnetic field processed (MFP)Bi2Sr2CaCu2O8+δ (Bi-2212) multifilamentary tapes in increasing and decreasing magnetic fields. The criticalcurrents are measured in magnetic fields up to 5 T at 4.2 K, with several orientations ofthe applied magnetic field relative to the tape plane. Two field dependences ofIc are found: a stronger one when the magnetic field is applied perpendicular to the tapeplane () and a weaker one when it is applied parallel to the tape plane . The angular dependence of Ic as a function of Bsinθ, which is the component of the magnetic field perpendicular to the tape plane, exhibits thatIc(Bsinθ) coincides with in the high-field region, indicating that the tape behaves as a two-dimensional (2D) superconductor.Because of the existence of misalignment in Bi-2212 grains, an average misalignment angleφavg is introduced and is found within the range of4.5°–6° for the MFPBi-2212 tape. φavg is independent of the magnetic field, indicating that it is an intrinsic property of the tape. Todetermine the critical current behaviour for all orientations of the magnetic field, a scaling functionf(θ) is introduced. The field-angle dependence of the critical current can be scaled to one curvewhere the field applied perpendicular to the tape plane at 4.2 K within the field rangebetween 0 and 5 T, both in increasing and decreasing fields, which is of primary importance.