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

Several workers have observed that, after fast field cooling of weak-linked granular high T_c type II superconductors, the diamagnetic magnetization will increase and trace a valley, hence a peak of enhanced Meissner effect, as the temperature approaches T_c during slow warming to the normal state with the applied field H_a 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 H_a, the extensive measurements of Jung et al on YBCO samples and the results of Hyun on compacted Nb₃Sn polycrystals.