The role of the intergranular and intragranular critical current densities in silver-sheathed Pb-Bi-Sr-Ca-Cu-O tapes is investigated by means of magnetic-moment measurements in perpendicular field at different temperatures using a superconducting quantum interference device magnetometer. We find that low-field magnetic-moment loops are mainly caused by the intergranular (transport) critical current density ${\mathit{J}}_{\mathit{c}}^{\mathit{J}}$ but that in high fields the contribution from the intragranular critical current density ${\mathit{J}}_{\mathit{c}}^{\mathit{G}}$ becomes significant. The low-field data can be described well in terms of a critical-state model for a thin strip of a homogeneous type-II superconductor in a perpendicular field where ${\mathit{J}}_{\mathit{c}}^{\mathit{J}}$ flows over the entire tape. The high-field data require in addition a description in terms of a critical-state model for the grains where ${\mathit{J}}_{\mathit{c}}^{\mathit{G}}$ circulates in each grain. Strong mechanical bending of the tape causes ${\mathit{J}}_{\mathit{c}}^{\mathit{J}}$ to disappear while ${\mathit{J}}_{\mathit{c}}^{\mathit{G}}$ is unaffected. The experimental data reveal the hysteretic nature of ${\mathit{J}}_{\mathit{c}}^{\mathit{J}}$ which is caused by the trapping of flux in grains. In all the tapes measured, ${\mathit{J}}_{\mathit{c}}^{\mathit{J}}$ is found to be much smaller than ${\mathit{J}}_{\mathit{c}}^{\mathit{G}}$. Comparing the remanent ${\mathit{J}}_{\mathit{c}}^{\mathit{J}}$ with ${\mathit{J}}_{\mathit{c}}^{\mathit{G}}$ in different tapes, we find that strong pinning in grains does not imply a high remanent intergranular critical current density.

• Received 13 April 1994

DOI:https://doi.org/10.1103/PhysRevB.50.10218