Proximity effect in superconducting-ferromagnetic granular structures

We examined the proximity effect in granular films made of Pb, a superconductor, and Ni, a ferromagnet, with various compositions. Slow decay of the critical temperature as a function of the relative volume concentration of Ni per sample was demonstrated by our measurements, followed by a saturation of Tc. Using an approximate theoretical description of our granular system in terms of a layered one, we show that our data can only be reasonably fitted by a trilayer model. This indicates the importance of the interplay between different ferromagnetic grains, which should lead to triplet Cooper pairing.