Non-equillibrium ultrafast optical excitation as a stimulus for ultra-small field-free magnetic skyrmions in ferrimagnetic GdFeCo

Abstract: Generating and manipulating magnetic skyrmions at ultrafast time scales is essential for future skyrmionbased racetrack memory and logic gate applications. Using the atomistic spin dynamics simulations, we demonstrate the nucleation of ultra-small field-free magnetic skyrmions in amorphous GdFeCo at picosecond timescales by femtosecond laser heating. The ultrafast nature of laser heating and subsequent cooling from a high-temperature state is crucial for forming magnetic skyrmion. The magnon localization and magnon coalescence are the key driving mechanisms responsible for stabilizing the magnetic skyrmions at zero field conditions. The polarization and, hence, the topological charge can be switched by exploiting the all-optical switching observed in GdFeCo. The skyrmion sizes and numbers can be controlled by varying pulse width and fluence of incident laser pulses. Applying an external magnetic field provides an additional degree of freedom to tune the skyrmion radius during the ultrafast optical creation of magnetic skyrmions. Our results provide a detailed understanding of the ultrafast creation of magnetic skyrmions using femtosecond laser pulses, a vital step in advancing next-generation skyrmion-based memory technologies.