Fig. 4. Typical magnetization dynamics in a Py disk after a femtosecond laser pulse quenching by micromagnetic simulation.

Snapshots of the magnetization dynamics during the formation of different magnetic structures in a triangular Py disk at different times after a femtosecond laser pulse excitation: (A) formation a single magnetic vortex state; (B) formation of a magnetic structure with two vortices; (C) formation of a magnetic structure with three vortices. The laser fluence is 12 mJ/cm². Note that the precise time scale of the magnetization relaxation process may vary (from hundreds of picoseconds to nanoseconds) with real ferromagnetic disk systems, which exhibit even more complex pinning mechanisms as well as temperature-dependent damping. The vortices and antivortices (including the half-antivortices indicated by the green half dots at the disk edge) in the different colored circles indicate the magnetic vortex-antivortex pairs that annihilate during the magnetization relaxation process. The blue and pink arrows indicate the spin pinning sites at the disk edge.