Dependence of transport critical current of magnetic field processed Bi2Sr2CaCu2O8/AgMg tapes on the background magnetic field and magnetic field direction

The background magnetic field dependence of the critical current ( I c ) is studied on magnetic field processed (MFP) Bi 2 Sr 2 CaCu 2 O 8+δ (Bi-2212) multifilamentary tapes in increasing and decreasing magnetic fields. The critical currents are measured in magnetic fields up to 5 T at 4.2 K, with several orientations of the applied magnetic field relative to the tape plane. Two field dependences of I c are found: a stronger one when the magnetic field is applied perpendicular to the tape plane ( ) and a weaker one when it is applied parallel to the tape plane . The angular dependence of I c as a function of B sinθ, which is the component of the magnetic field perpendicular to the tape plane, exhibits that I c ( B sinθ) 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 angle φ avg is introduced and is found within the range of 4.5°–6° for the MFP Bi-2212 tape. φ avg is independent of the magnetic field, indicating that it is an intrinsic property of the tape. To determine the critical current behaviour for all orientations of the magnetic field, a scaling function f (θ) is introduced. The field-angle dependence of the critical current can be scaled to one curve where the field applied perpendicular to the tape plane at 4.2 K within the field range between 0 and 5 T, both in increasing and decreasing fields, which is of primary importance.