  Epitaxially grown multilayer systems offer the possibility to study the
influence of ferromagnetism on superconductivity in a new and controlled way.
In this paper, we explore how the superconducting properties of high quality,
epitaxially-grown superconductor/normal-metal/ferromagnet trilayers evolve as a
function of the exchange splitting in the ferromagnet, and the thickness of the
normal metal layer. We report results for Nb(110)/Au(111)/Co(0001), and make a
detailed comparison with earlier results for Nb(110)/Au(111)/Fe(110). We use
quantitative FFT analysis to confirm the existence of a long-period (2.1 nm)
oscillation in the superconducting transition temperature Tc as a function of
the Au-layer thickness tAu, for tAu>2 nm, and highlight an additional
short-period (0.76 nm) oscillation for tAu<3 nm in Nb/Au/Co. This short-period
oscillation can be explained in terms of a damped RKKY-like oscillation of the
spin-polarization in Au. The robustness of the long-period oscillation against
the substitution of Co for Fe suggests that it is intrinsic to the Au(111)
layer on Nb, and may represent a new form of quantum interference in very clean
trilayer systems.
