Exchange coupling between iron layers separated by bcc copper

The exchange coupling between Fe layers separated by bcc Cu is calculated for Fe/Cu/Fe (001) trilayers. It is shown that the coupling is basically regulated by three extrema of the bulk bcc Cu Fermi surface. The contributions from those extrema are all of the same order of magnitude, but that associated with the ``belly'' at the Γ point dominates. The calculated temperature dependence of the coupling varies considerably with spacer layer thickness. Individually, the amplitudes of these extrema contributions decrease with temperature, each according to a different rate. Such an effect may cause an actual increase of coupling with temperature for some Cu thicknesses.