The low-field peak in magnetization loops of uniform and granular superconductors in perpendicular magnetic fields

The present work aims to explain the anomalous position of the low-field pe ak in magnetization loops in Bi-2223 tapes, where the peak is often seen sh ifted to a positive field on the descending field branch. We prove theoreti cally that for an infinitely thin and long strip placed in a perpendicular field, the central peak occurs exactly at 0 T, for any function J(c)(B). Th is general result is shown to be in excellent agreement with experimental d ata. After introducing granularity in such a film into a lattice of small w eakly-overlapping disks, the peak becomes shifted to positive values. We co nclude that this anomalous behaviour in the magnetization is a definite sig nature of granularity.