Exchange coupling between iron layers separated by silver and gold

The exchange couplings between bcc Fe layers separated by fee Ag and Au are calculated for Fe/Ag/Fe and Fe/Au/Fe (001) trilayer structures as functions of the spacer thickness for several temperatures. The calculated couplings show a short-period oscillatory behavior in Fe/Au for all temperatures investigated. For Fe/Ag a long period prevails for temperatures T greater than or equal to 300 K, but at T=0 a strong short-period contribution is present for Ag thicknesses greater than or equal to 30 atomic planes. These results are in very good agreement with finite-temperature experiments, but the coupling strengths as calculated by assuming perfect interfaces are much larger than those observed. It is shown that interplanar distance relaxation at the interfaces leads to a rather large effective change of the coupling amplitude in Fe/Au for Au thicknesses less than or equal to 20 atomic planes, but mainly causes a phase shift in the oscillatory coupling for Fe/Ag. It is found that interfacial interdiffusion substantially reduces the amplitude of the coupling in Fe/Au/Fe, but not much in Fe/Ag/Fe.