Spin-wave focusing induced skyrmion generation

Abstract

We propose a method to generate magnetic skyrmions through spin-wave focusing in chiral ferromagnets. A lens is constructed to focus spin waves by a curved interface between two ferromagnetic thin films with different perpendicular magnetic anisotropies. Based on the principle of identical magnonic path length, we derive the lens contour that can be either elliptical or hyperbolical depending on the magnon refractive index. Micromagnetic simulations are performed to verify the theoretical design. It is found that under proper conditions, magnetic skyrmions emerge near the focus point of the lens where the spin-wave intensity has been significantly enhanced. A close investigation shows that a magnetic droplet first forms and then converts to the skyrmion accompanied by a change in topological charge. The phase diagram about the amplitude and time duration of the exciting field for skyrmion generation is obtained. Our findings would be helpful for designing spintronic devices combining the advantages of skyrmionics and magnonics.