  In this paper we show that the phase shift of the spin waves can be
controlled in transmission through metasurface represented as an ultra-narrow
non-magnetic spacer separating two ferromagnetic films. We design this
metasurface to present the focusing of spin waves in an Co thin film. For this
purpose we exploit the strength of the interlayer exchange coupling
interactions of RKKY type which allows to control the phase of the transmitted
and reflected spin waves in the wide range of angles [$-\pi/2$;$\pi/2$]. We
combined this phase-shift dependency with the lens equation to demonstrate
numerically the lens for spin waves based on ultra-narrow metasurface.
