Oscillatory Interlayer Exchange Coupling with the Cu Cap Layer Thickness in Co/Cu/Co/Cu(100)

An oscillatory dependence of the strength of the antiferromagnetic exchange coupling on the cap layer thickness has been observed in an epitaxial Co/Cu/Co/Cu(100) sample with a wedge-shaped Cu interlayer and cap layer. The result is consistent with a single long oscillation period stemming from the extremal spanning vector of the Cu (cap layer) Fermi surface along the $\Gamma X$ line. The absence of a short period oscillation is understood from the confinement of the corresponding electron states to the spacer. A quantitative comparison with Bruno's model is made.