Probe and control of photo-excited magnetization precession in Co/Pd multilayer films at low laser fluence regime

We present femtosecond-pulse-induced precession of magnetization at low laser fluence ( < 5 μ J / cm 2) regime as a function of magnetic field and laser fluence in three Co/Pd multilayer (ML) systems. These systems belong to three different regimes of magnetic anisotropy that vary with Co thickness (t C o): in-plane (sample 1, t C o = 0.74 nm), weakly out-of-plane (sample 2, t C o = 0.6 nm), and out-of-plane (sample 3, t C o = 0.40 nm). Interestingly, we observed that the precession amplitudes increase significantly with decreasing the Co layer thickness. In this study, the influence of various spin dynamics and static magneto-optical parameters on precession amplitude is examined critically and compared with a previously proposed analytical expression that connects those quantities. It is found that the enhancement of structural-dependent energy transfer efficiency between charge and spin subsystems is indeed responsible for the observed variations in precession amplitudes. On the basis of this fact, we discuss that the spin–orbit interaction that yields perpendicularly spin-polarized electrons in the MLs through the Co/Pd interface is responsible for the observed increase in precession amplitudes of locally excited magnetization. Our approach of employing low-fluence laser excitation of magnetization precession could be practical for developing a non-thermal, all-optical magnetic switching toward photonic memory applications.