Contribution of quantum-well states to the RKKY coupling in magnetic multilayers

We calculate the RKKY coupling between two magnetic layers separated by a nonmagnetic spacer, with scattering potentials added to represent changes in environment between the layers. For the case of a spacer potential well of depth V, the usual π/${\mathit{k}}_{\mathit{F}}$ oscillation period is superseded by one much longer, πħ/ √2mV . For a deep potential well (V∼${\mathrm{\varepsilon }}_{\mathit{F}}$), the RKKY interaction becomes purely ferromagnetic for spacings greater than a few angstroms. Scattering potentials localized at the interfaces produce a phase shift in the RKKY oscillations. We discuss evidence for these effects in experimental systems.