Figure 3: Magnetization as a function of time delay for the [Co−Pd]30 multilayer film.

(a) Demagnetization curves obtained for different pump fluences: 4, 6, 7.5 and 9 mJ cm⁻² (respectively; red, up; green, down; cyan, right; and purple, left triangles). The probe fluence, 5×10⁻⁵ mJ cm⁻², is negligible compared with the pump fluence²⁶. The solid lines represent the best fits obtained for each fluence. The characteristic thermalization times, τ_th, found are all between 90 and 110 fs with an error of ±25 fs. No clear relation between the pump fluence and τ_th has been observed. (b) Example of a long delay scan used to determine the spin-phonon relaxation constant, τ_s−ph. Long delay scans have been performed for each fluence. (c) High-resolution demagnetization curve obtained for the highest possible pump fluence (11 mJ cm⁻²), yielding a demagnetization of 44% and clearly showing a thermalization time of ~100 fs. The red solid lines in panels (b) and (c) represent the best fits obtained. The dashed lines in panels (a) and (c) indicate the demagnetization times, τ_th, of about 100 fs.