Variation of the superconducting coherence length in Superconductor/Ferromagnet bilayers

Full text: Superconductor-ferromagnet metallic S/F hybrids recently became an object of the intensive investigations. On the one hand, a very interesting physics of this objects attract attention of the researchers, on the other hand the perspectives of technical applications for spintronic devices make them attractive for engineers. In the layered S/F hybrids superconducting condensate penetrates through the S/F interface into a ferromagnetic layer, and the pairing wave function not only decays deep into the F metal, but simultaneously oscillates, as the result of the influence of the exchange field of ferromagnetic layer on the cooper pairs. Investigation of the critical magnetic fields of the layered S/F hybrids demonstrates that not only the superconducting carriers, cooper pairs, are influenced by the ferromagnet, but also the nonsuperconducting carriers, electrons, are affected. The dimensional 2D-3D crossover of the critical magnetic field and the shift of the crossover temperature, as the result of the changes of the interface transparency for the carriers, was detected recently in SF-hybrids. In this work we report on the experimental observation of the coherence length variation (calculated from the temperature dependence of the upper critical fields investigation) in Nb/Cu1-xNix bilayers as a function of the ferromagnetic layer thickness dCuNi for a set of samples with constant Nb layer thickness. The coherence length was calculated from the slope of the dBc2(T)/dT dependences near Tc, as: ξGL(0) = (- (dBc2(T)/dT)(2πTc/φ0))-1/2. Our experiments give evidence for a strong influence of the ferromagnet layer presence on the coherence length: it.s value anomalous increases with the ferromagnet layer thickness increase. The detailed theoretical consideration of the observed effect is necessary as the next step of S/F hybrids investigation. (authors)