Manifestation of New Interference Effects in a Superconductor-Ferromagnet Spin Valve

Superconductor-ferromagnet (S/F) spin valve effect theories based on the S/F proximity phenomenon assume that the superconducting transition temperature T-c of F1/F2/S or F1/S/F2 trilayers for parallel magnetizations of the F1 and F2 layers (T-c(P)) are smaller than for the antiparallel orientations (T-c(AP)). Here, we report for CoOx/Fe1/Cu/Fe2/In multilayers with varying Fe2-layer thickness the sign-changing oscillating behavior of the spin valve effect Delta T-c = T-c(AP) - T-c(P). We observe the full direct effect with T-c(AP) > T-c(P) for Fe2-layer thickness d(Fe2) < 1 nm and the full inverse (T-c(AP) < T-c(P)) effect for d(Fe2) >= 1 nm. Interference of Cooper pair wave functions reflected from both surfaces of the Fe2 layer appear as the most probable reason for the observed behavior of Delta T-c.