Reentrant superconductivity in Nb/Cu1-xNix bilayers

We report on the first observation of a pronounced reentrant superconductivity phenomenon in a superconductor/ferromagnet layered system. The results were obtained using a superconductor/ferromagnetic-alloy bilayer of Nb/Cu1-xNix. The superconducting transition temperature Tc drops sharply with increasing thickness dCuNi of the ferromagnetic layer, until complete suppression of superconductivity is observed at dCuNi≈4nm. Increasing the Cu1-xNix layer thickness further, superconductivity reappears at dCuNi≥13nm. Our experiments give evidence for the pairing function oscillations associated with a realization of the quasi-one-dimensional Fulde-Ferrell-Larkin- Ovchinnikov-like state in the ferromagnetic layer. © 2006 The American Physical Society