Highly Nonreciprocal Spin Waves Excited by Magnetoelastic Coupling in a Ni/Si Bilayer

We demonstrate a largely enhanced nonreciprocal propagation of spin waves (SWs) magnetoelastically excited in $\mathrm{Ni}$/$\mathrm{Si}$ bilayer films. The nonreciprocity is attributed to the shear component of the strain tensor, which can be enlarged by increasing the thickness of the $\mathrm{Si}$ layer. By evaporating a 400-nm-thick $\mathrm{Si}$ layer on a $\mathrm{Ni}$ film, we enhanced the nonreciprocal ratio by up to 1200%. This finding paves the way for rectification of SWs in magnonic devices.