Ferromagnetic proximity effect in a-CoxSi1−x/Nb bilayers: Role of magnetic disorder and interface transparency

Abstract

The superconducting and magnetic properties of a-CoxSi1−x /Nb bilayers have been studied as a function of Co content in order to analyze the superconducting/ferromagnetic proximity effect in a system with strong disorder in the magnetic layers. As Co atoms become more diluted, the magnetization of the amorphous a-CoxSi1−x alloy decreases gradually, whereas their resistivity increases and enters in a weak localization regime. The superconducting transition temperatures of the a-CoxSi1−x /Nb bilayers follow a decreasing trend as Co content is reduced, reaching the lowest value at the boundary between the ferromagnetic-nonmagnetic amorphous phases. These results can be understood in terms of the increase in interface transparency together with the changes in the spin-flip scattering term as magnetic disorder increases and the amorphous a-CoxSi1−x layers loose their magnetic character.