Intragranular critical current density of superconductor grain in screen-printed Ag-Bi2223 tape

Transport critical current density J(c)(J) is investigated as a function of the external magnetic field perpendicular to a sample surface, and the tra pped magnetic field and magnetisation in a remanent state after a removal o f external field are also investigated at 77 K on screen-printed Ag-Bi2223 composite tape. The hysteresis behaviour in J(c)(J) between increasing and decreasing fields is observed in a zero-field-cooled sample and explained b y the influence of trapped magnetic flux in the grains on intergranular (tr ansport) current. Such hysteresis in J(c)(J) causes decreases in the trappe d field and in magnetisation with increasing B-ex*, defined as the maximum field in a field loop for measuring J(c)(J) values. The experimental result s give the full flux penetration field B-p for the grains to be nearly equa l to 9 mT. The use of a critical state model and the value of B-p = 9 mT re sults in the intragranular critical current density J(c)(G) being similar t o 5000 A/mm(2), which is about 50 times higher than the transport current d ensity (similar to 85 A/mm(2) at 77 K and self-held) of the sample. The stu dy shows that strong pinning in the grains does not lead to a high transpor t critical current density unless further improvement for grain connectivit y is made. (C) 1999 Cryogenic Association of Japan. Published by Elsevier S cience Ltd. All rights reserved.