  We have investigated CuNi/Nb/CuNi trilayers, as 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, Tc, of the superconducting Nb. After
reproducing a Tc shift of a few mK, we have gone on to explore the performance
limits of the structure. The results showed the Tc shift 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 were the main features limiting the Tc shift.
