Quantum-well states and exchange coupling in fcc (111) magnetic multilayers

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Abstract
In the Ruderman-Kittel-Kasuya-Yosida (RKKY) approach to oscillatory exchange coupling in magnetic multilayers, the oscillation period may be determined from the bulk spacer Fermi surface by inspection. In the quantum-well theory of exchange coupling this is only possible for simple cases and no such recipe exists for fcc (111) multilayers, for example. The correct procedure for this fcc (111) case, which is relevant to the interesting Co/Cu (111) system, is established. The subtle manner in which the RKKY period is recovered in this case is explained. The equality of the RKKY and quantum-well periods is proved for any single-band tight-binding model with hopping normal to the layers restricted to nearest-neighbor planes.