Micro-Focused Pulse Laser-Induced Propagating Spin Waves in Permalloy Films With Different Thicknesses

Propagating spin waves excited by a micro-focused ultra-short pulse laser were investigated in Permalloy films with the thicknesses of 20, 50, and 100 nm by means of an all-optical space-and-time-resolved magneto-optical Kerr effect. Although various perpendicular standing spin-wave modes were excited, the propagating magneto-static surface spin wave was clearly detected in each film, where the group velocities of approximately 4, 8, and 12 km/s and the propagation lengths of 3.8, 6.6, and 13 ${\mu }\text{m}$ for the 20, 50, and 100 nm-thick films, respectively, were evaluated. The evaluated group velocities were consistent with the theoretical values, whereas the propagation lengths were smaller than the theoretical values with the Gilbert damping constant ${\alpha }$ of 0.008.