  Superconducting spin valves based on the superconductor/ferromagnet (S/F)
proximity effect are considered to be a key element in the emerging field of
superconducting spintronics. Here, we demonstrate the crucial role of the
morphology of the superconducting layer in the operation of a multilayer
S/F1/F2 spin valve. We study two types of superconducting spin valve
heterostructures, with rough and with smooth superconducting layers, using
transmission electron microscopy in combination with transport and magnetic
characterization. We find that the quality of the S/F interface is not critical
for the S/F proximity effect, as regards the suppression of the critical
temperature of the S layer. However, it appears to be of paramount importance
in the performance of the S/F1/F2 spin valve. As the morphology of the S layer
changes from the form of overlapping islands to a smooth case, the magnitude of
the conventional superconducting spin valve effect significantly increases. We
attribute this dramatic effect to a homogenization of the Green function of the
superconducting condensate over the S/F interface in the S/F1/F2 valve with a
smooth surface of the S layer.
