Low-Power Photo-Induced Precession of Magnetization in Ultra-Thin Co/Pd Multilayer Films

Photo-induced precession of magnetization (PIPM) has been studied in ultra-thin [Co/Pd]₅ multilayered structures at the region of pump fluences F = 0.11 to 11 μJ/cm². In a series of samples with t_pd = 1.62 nm, precession amplitude has increased at t_Co = 0.86 nm, around which magnetic anisotropy changes between in-plane (tCo > 0.86 nm) and out-of-plane (t_Co ≤ 0.86 nm). When t_Pd was reduced in half (tpd = 0.81 nm) the amplitude of PIPM has increased significantly, which leads us to the observation of PIPM at F = 0.25 μJ/cm², the regime of low energy excitation. A model which connects precession amplitude and parameters associated with spin dynamics has been developed, through which efficiency of energy transfer between electron and spin subsystems has been examined quantitatively.