Enhancement of the Meissner effect upon the warming of fast field cooled weak-linked granular high Tc superconductors: a simple model

Several workers have observed that, after fast field cooling of weak-linked granular high Tc type II superconductors, the diamagnetic magnetization will increase and trace a valley, hence a peak of enhanced Meissner effect, as the temperature approaches Tc during slow warming to the normal state with the applied field Ha kept fixed throughout the temperature excursion. We present a simple extension to interconnected granular systems of the established model for isotropic single crystals which qualitatively and quantitatively reproduces our observations of this phenomenon over a large range of Ha, the extensive measurements of Jung et al on YBCO samples and the results of Hyun on compacted Nb3Sn polycrystals