Upon the addition of Ag impurities in the Co layers of high quality mo
lecular-beam-epitaxy grown Co/Cu(111) trilayers, the antiparallel coup
ling observed in the Co/Cu/Co trilayers for t(Cu) < 12 Angstrom has be
en transformed to a parallel coupling which appears as a significant s
hift in the phase of the interlayer coupling. In addition, the amplitu
de of the exchange coupling oscillations appears to decrease exponenti
ally with increasing Cu layer thickness.