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

Spin-wave (SW) or its quantum, magnon, is studied with renewed interest as a basis for wave-based classic information processing. Along with other physical waves, SWs also have wave-like properties, such as radiation, propagation, reflection, and refraction, which have been extensively investigated in order to manipulate SWs. Especially, there have been many methods reported to focus the SW via a nonlinearity, a graded refractive index, and a phase-controlled SW sources. In this work, we explore another efficient way of the SW focusing by using the spatially and temporally tailored magnetic field excitations. Using a micro-magnetic simulation, we explain how the SW propagates and is focused in a ferromagnetic thin film with a perpendicularly magnetized anisotropy after its excitation by a pulsed magnetic field having a flat-top amplitude distribution. In particular, we observe that the focusing appears more efficiently in the multi-domain state divided by Bloch walls compared to that in the single-domain state. Based on these results, we suggest the flat-top excitation of the magneto-static wave as an efficient way to create magnetic droplets in a multi-domain state of a perpendicularly magnetized system.