Impact of the inverse Faraday effect in the ultrafast magnetization dynamics of Au/YIG bilayers

The inverse Faraday effect (IFE) is a magneto-optical phenomenon in which circularly polarized (CP) light induces magnetization in a material. Due to its inherent speed, the IFE is a promising candidate for advancing all-optical switching in opto-spintronic devices. In this study, we investigate the effects of CP light on gold–yttrium iron garnet (Au/YIG) thin film bilayers using ultra-fast pump-probe time-resolved magneto-optical Kerr effect (TR-MOKE) experiments. By illuminating the gold film with circularly polarized light (λ = 800 nm), we induce spin polarization via the IFE, which subsequently transfers spin angular momentum to the iron garnet. This spin injection competes with the thermal spin current generated by the longitudinal spin Seebeck effect (LSSE). We analyze the contributions of both spin currents—IFE and LSSE—and their respective roles in the ultrafast magnetization dynamics of this bilayer system. The results provide deeper insights into ultrafast magnetization processes under the influence of multiple magneto-optical effects.