Subtle interface magnetism of Fe/Au multilayers

By ab initio LMTO calculations in atomic-sphere approximation we have studied the interlayer exchange coupling between Fe films separated by Au spacers in infinite Fe/Au multilayers with (001) interface orientation. We also performed detailed calculations of the magnetization and charge profiles across the system. We find an enhancement of the Fe moments at the interface, which amount to $\approx 2.8$ $\mu_B$ instead of the bulk value of 2.2 $\mu_B$, and we also find a slight magnetic polarization of the order of 0.01 $\mu_B$ at the Au interface layers. These results do not depend sensitively on the lattice constants assumed in the calculation. When we try to optimize our results with respect to the ratio $R_{Fe}/R_{Au}$ of the Wigner-Seitz spheres for the mutual components, we often find the optimum near charge neutrality of the interface monolayers: However, this is not always the case, and usually the sign and the magnitude of the exchange coupling depend sensitively on the optimal choice of the above-mentioned ratio. In particular, for Fe$_5$/Au$_3$ we find an anomaly with a large dipole moment at the interface and a related anomaly of the exchange coupling.