Superconductor-ferromagnet CuNi/Nb/CuNi trilayers as superconducting spin-valve core structures

We have investigated CuNi/Nb/CuNi trilayers, as they have been recently used as the core structure of a spin-valve-like device [J. Y. Gu et al., Phys. Rev. Lett. 89, 267001 (2002)] to study the effect of magnetic configurations of the CuNi layers on the critical temperature, T-C, of the superconducting Nb. After reproducing a T-C shift of a few mK, we have gone on to explore the performance limits of the structure. The results showed the T-C shift that we found to be quite close to the basic limits of this particular materials system. The ratio between the thickness and the coherence length of the superconductor and the interfacial transparency was the main feature limiting the T-C shift.