Spin wave collimation using a flat metasurface.

In this paper, we show that the phase shift of spin waves propagating in the plane of the film can be controlled by a metasurface formed by an ultra-narrow non-magnetic spacer separating edges of the two thin ferromagnetic films. For this purpose, we exploit the strength of the exchange coupling of the RKKY type between the films which allows tuning the phase of the transmitted spin waves in the wide range of angles [-π/2; π/2]. We combined the phase-shift dependency along the interface with the lens equation to demonstrate numerically the metalens for spin waves.