Unveiling laser-induced ultrafast switching mechanism in ferromagnetic spin valves

Abstract

The recent demonstration of single-shot ultrafast magnetization reversal in ferromagnetic spin valves—combining spin-transfer torque with optically induced ultrafast switching—has offered a promising avenue for next-generation magnetic storage technologies. However, a comprehensive theoretical framework is currently lacking to validate and elucidate the reversal mechanisms across different initial magnetic states. Here, we develop a theoretical model for optically induced ultrafast magnetization reversal by integrating the s-d exchange model with an atomistic spin dynamics approach. The proposed model's validity is corroborated through detailed comparisons with experimental time-resolved magneto-optic Kerr effect data. Our findings highlight distinct contributions from ultrafast demagnetization and ultrafast spin currents to the switching process. Furthermore, we systematically explore the influence of laser pulse parameters, such as fluence and width, as well as material-specific properties like magnetic anisotropy and Gilbert damping coefficients on ultrafast ferromagnetic reversal. Our findings indicate that increasing laser pulse fluence intensifies ultrafast demagnetization and enhances spin current strength, whereas extending pulse width delays demagnetization and diminishes spin current intensity. Notably, magnetic anisotropy exerts minimal influence on spin current generation, while higher damping coefficients amplify spin current intensity, thereby facilitating ultrafast reversal. Comparative simulations across various spin valve materials reveal that CoFe exhibits superior ultrafast spin current conversion efficiency compared to [Co/Ni]n and CoPt-based systems. This work establishes a robust theoretical framework for optically induced ultrafast magnetization reversal and provides critical insights for the design of future picosecond-scale, low-power, and nonvolatile magnetic recording devices.