  We have measured a long-range supercurrent in Josephson junctions containing
Co (a strong ferromagnetic material) when we insert thin layers of either PdNi
or CuNi weakly-ferromagnetic alloys between the Co and the two superconducting
Nb electrodes. The critical current in such junctions hardly decays for Co
thicknesses in the range of 12-28 nm, whereas it decays very steeply in similar
junctions without the alloy layers. The long-range supercurrent is controllable
by the thickness of the alloy layer, reaching a maximum for a thickness of a
few nm. These experimental observations provide strong evidence for induced
spin-triplet pair correlations, which have been predicted to occur in
superconducting/ferromagnetic hybrid systems in the presence of certain types
of magnetic inhomogeneity.
