Enhancement of a spin-wave self-focusing by a pulsed flat-top excitation field in a multi-domain state

Abstract

We investigate a spin-wave (SW) self-focusing in a ferromagnetic FePd thin film with a perpendicular magnetic anisotropy by using micro-magnetic simulation. In a one-dimensional structure, a point-excitation of forward volume magnetostatic waves leads the SW propagation in the form of a wave packet. When SWs are excited over a wide area with a uniform amplitude distribution, the SW propagation occurs by taking not only a diverging component but also a focusing-like component. Interestingly, we can increase the focusing effect by reflecting the diverging waves at the magnetic phase boundary, such as domain walls. This SW focusing appears also in a two-dimensional system, and, furthermore, magnetic droplets can be easily formed at the focal points when the focused SW intensity exceeds an appropriate threshold. Based on these results, we can propose the flat-top excitation of the magnetostatic waves as an efficient way to generate the SW self-focusing and also to create magnetic droplets in a multi-domain state of perpendicularly magnetized systems.