Unique features of the Gilbert damping in magnetic multilayers were
investigated by ferromagnetic resonance (FMR) using magnetic single and
double layer structures prepared by molecular beam epitaxy. The FMR
linewidth for the Fe films in the double layer structures was larger
than the FMR linewidth in the single Fe films having the same thickness.
The additional FMR linewidth scaled inversely with the film thickness,
and increased linearly with increasing microwave frequency. These
results demonstrate that a transfer of electron angular momentum between
the magnetic layers leads to additional relaxation torques.