  Propagation of backward magnetostatic surface spin waves (SWs) in exchange
coupled Co/FeNi bilayers are studied by using Brillouin light scattering (BLS)
technique. Two types of SWs modes were identified in our BLS measurements. They
are magnetostatic surface waves (MSSWs) mode and perpendicular standing spin
waves (PSSWs) mode. The dispersion relations of MSSWs obtained from the Stokes
and Anti-Stokes measurements display respectively positive and negative group
velocities. The Anti-Stokes branch with positive phase velocities and negative
group velocities, known as backward magnetostatic surface mode originates from
the magnetostatic interaction of the bilayer. The experimental data are in good
agreement with the theoretical calculations. Our results are useful for
understanding the SWs propagation and miniaturizing SWs storage devices.
