Long and Short Range Oscillatory Exchange Coupling in Fe/Cu and Co/Cu Magnetic Multilayers

By carrying out accurate first-principles superlattice calculations, we determined the exchange coupling in bcc Fe/Cu and fcc Co/Cu multilayers as a function of the Cu spacer thickness. The fact that we can obtain long-range oscillatory coupling directly from first principles suggests that our theoretical model includes the underlying physical mechanism, and that such coupling is indeed a band structure effect. The exchange coupling depends on the interfacial orientation as well as on the Cu spacer thickness. In bcc [001] Fe/Cu, fcc [001] Co/Cu, and fcc [110] Co/Cu, the coupling has both long and short-range oscillatory components, while in fcc [111] Co/Cu, the long-range component dominates. Using a simplified model for the Fermi surface of the Cu spacer, we can relate the short-range oscillations to electronic transitions across the Fermi sphere, and the long-range oscillations to electronic transitions between spheres in adjacent zones in extended k-space, i.e., to interzonal transitions.