Photo-excited Magnetization Precession in Co/Pd Multilayer Films at Low Laser Fluence Regime*

In this study, we present optically induced precession of magnetization at low laser fluence regime, as a function of magnetic field, in three Co/Pd multilayer (ML) systems. The Co/Pd MLs studied here have three different regimes of magnetic anisotropy (In-Plane, weak out-of-plane, and out-of-plane) and our results provided a better understanding of the relationship between optically excited precession of magnetization and the interface anisotropy, of Co/Pd multilayers. We will discuss the connection of precession frequency and amplitude, Gilbert damping, gyromagnetic ratio, in our MLs, to their thickness. We have identified that spin-orbit interactions, affecting perpendicularly spin-polarized electrons at the Co/Pd interface, to be the dominant mechanism for our observed variation in the oscillation's amplitude of locally excited magnetization. There has been little study on the low fluence regime (< 10 µJ/cm²) and our approach could be a practical method for developing a non-thermal all-optical magnetic switching toward low-power magnetic memory applications.