Intragranular critical current density in Ag-sheathed (Bi, Pb)2Sr2Ca2Cu3 Ox tapes

Abstract

Transport critical current density JJc as a function of external magnetic field perpendicular to a tape surface is investigated for Ag-sheathed (Bi,Pb)2Sr2Ca2Cu3Ox monofilamentary tapes at 77 K. The history effect of JJc on the magnetic field between increasing and decreasing fields is observed in a zero-field-cooled sample and is interpreted by the influence of trapped magnetic fields in grains on the intergranular (transport) current. The experimental results reveal the full flux penetration field Bp for the grains. Using a critical state model and the value of Bp, the intragranular critical current density JGc is estimated to be ~5000 A mm-2, which is nearly the same value among all samples and much larger than the value of JJc. The present study shows that the current carrying capacity for the tape is limited by the weak links at grain boundaries, and strong pinning in grains does not lead to a high transport critical current density unless further improvements in grain connectivity are made.