The first direct evidence of oscillatory coupling in Co/Au(111)/Co trilayers grown in ultrahigh vacuum is reported. For samples with identical cobalt layer thicknesses, up to three peakjs of magnetoresistance, corresponding to antiferromagnetic coupling between the cobalt layers, are observed with increasing gold spacer layer thickness, ${\mathit{t}}_{\mathrm{Au}}$. By growing trilayers with different cobalt coercive fields, a direct measurement of both ferromagnetic and antiferromagnetic coupling as a function of ${\mathit{t}}_{\mathrm{Au}}$ was possible. The experimental data are in good agreement with theoretical predictions.

• Received 7 July 1993

DOI:https://doi.org/10.1103/PhysRevLett.71.3023