Femtosecond-laser-induced reversal in in-plane-magnetized spin valves

Ultrashort spin-polarized electron pulses, generated through optically driven ultrafast demagnetization, have demonstrated high efficiency in achieving magnetization reversal of a ferromagnetic layer within a few hundred femtoseconds. Previous studies have focused on magnetization reversal in perpendicularly magnetized spin valves, where the static magnetization configuration and its dynamics are strongly influenced by the substantial demagnetization field inherent in this geometry. Consequently, the impact of layer thickness on the reversal process in such configurations presents a significant challenge and has been rarely studied. Here, we investigate in-plane magnetized $\mathrm{Gd}\mathrm{Co}/\mathrm{Cu}$/ferromagnetic layer spin valves in relation to isolating the impact of the Curie temperature and the ferromagnetic layer thickness on magnetization switching. We demonstrate that the threshold laser fluence necessary for reversing the ferromagnetic layer increases with the Curie temperature and the ferromagnetic layer thickness. Additionally, our findings indicate that achieving complete reversal may require multiple pulses, with the number of pulses needed increasing with the Curie temperature and the thickness of the ferromagnetic layer. The maximum thickness of the ferromagnetic layer that allows for full reversal is limited by the $\mathrm{Gd}$ concentration in the $\mathrm{Gd}\mathrm{Co}$ spin current source layer. These results enhance our understanding of ultrafast magnetization reversal induced by ultrafast spin pumping and offer valuable insights for designing energy-efficient magnetic memory devices.