Role of superconductor normal metal superconductor proximity junctions in governing the intergranular flux pinning in electrophoretically deposited Y-Ba-Cu-O films

Within a low-field limit, the magnetic critical current density (J(c)) is found to have dropped drastically in case of thinner Y-Ba-Cu-O films (less than or equal to 20 mu m); deposited electrophoretically on silver substrates. In this low-field limit, the current loops scale the entire sample volume consisting of grain-grain-boundary networks. Due to the presence of uniformly distributed silver at the grain boundaries within the entire network (in case of these thinner films), the pinning potential (U-0) of the grain boundary Josephson vortices is small as it depends on random variation in Josephson coupling energy (E(J)) of the grain boundaries. In case of thicker films, of course, U-0 can be high as no silver penetration is possible up to the top layers and hence, U-0 varies as similar to d(0.4) (d=film thickness) and ranges from 45 to 135 meV over a thickness regime of 3-65 mu m. Consequently, the magnetic J(c) too, follows an anomalous trend of variation with film thickness.