Interference effects of the superconducting pairing wavefunction due to the Fulde–Ferrell–Larkin–Ovchinnikov like state in ferromagnet/superconductor bilayers

The theoretical description of the Fulde–Ferrell–Larkin–Ovchinnikov like state establishing in nanostructured bilayers of ferromagnetic (F) and superconducting (S) material leads to critical temperature oscillations and reentrant superconductivity as the F layer thickness gradually increases. The experimental realization of these phenomena is an important prerequisite for the fabrication of the ferromagnet/superconductor/ferromagnet core structure of the superconducting spin-valve. A switching of the spin-valve is only expected if such non-monotonic critical temperature behavior is observed in F/S bilayers as well as in the S/F bilayers, a combination of which the spin-valve core structure can be regarded to consist of. In our former investigations we could demonstrate the required non-monotonic behavior of the critical temperature in S/F bilayers. In this study we succeeded in the preparation of F/S bilayers, where the superconducting material is now grown on top of the ferromagnetic metal, which shows deep critical temperature oscillations as a function of the ferromagnetic layer thickness as well as an extinction and recovery, i.e. a reentrant behavior, of superconductivity. In particular, the latter is necessary to obtain a spin-valve with a large critical temperature shift between the parallel and antiparallel configurations of magnetizations in the F layers.