Fig. 3: Spin polarized hot electron induced dynamics at Fe L₃ edge.

Normalized time-resolved measurements of Fe L₃ XMCD at laser fluence of 120 mJ/cm² (absorbed fluence F_abs = 3.2 mJ/cm²) at T = 80 ± 20 K. To distinguish the SPHE effect, measurement is done in two configurations: Magnetization of Co is parallel (P) (blue curve) and Antiparallel (AP) (red curve) to Fe magnetization. Solid lines are the exponential fit with Gaussian convolution. The fitting of the P and AP experimental curves show characteristic demagnetization times of 470 ± 80 fs, resp. 550 ± 80 fs. a At a short time scale, i.e., below 2 ps, dynamics in the P case is faster and shows more demagnetization than AP case. The red Gaussian curve represents the SPHE pulse shape, arriving at the Fe₇₄Gd₂₆. The error bars obtained for the TR-XMCD at the Fe L₃ edge as shown in (a) are given by the standard deviation of the experimental data with respect to the fitting functions. Inset: The hysteresis measured at the Co and Fe L₃ resonance edges as measured in the normal hybrid mode at the femtoslicing beam line. This indicates that the coercivity of Co/Pt layer (H_C = 550 Oe) is larger than the FeGd (H_C = 100 Oe) and ensures the maximum spin polarization from Co/Pt. b Normalized difference of the demagnetization dynamics between the P and AP cases obtained at the Fe L₃ edge (open symbols) superposed to the smoothed data obtained by averaging over adjacent 15 points (magenta dotted line). The solid black line is the normalized difference between both fitted dynamics (P and AP exponential fitted curves) as shown in (a) by solid black lines. A maximum for the difference between both cases is found around 0.5 ps. c Dynamics at a longer time scale. SPHE effect vanishes after 2 ps due to limited mean free path and lifetime of those SPHEs.