  All-optical control dynamics of magnetization in sub-10 nm metallic thin
films are investigated, as these films with quantum confinement undergo unique
interactions with femtosecond laser pulses. Our theoretical derivations based
on the free electron model show that the density of states at Fermi level
(DOS_F) and electron-phonon coupling coefficients (G_ep) in ultrathin metals
have very high sensitivity to film thickness within a few Angstroms. As DOS_F
and G_ep depend on thickness, we show that completely different magnetization
dynamics characteristics emerge compared with bulk metals. Our model suggests
highly-efficient energy transfer from fs laser photons to spin waves due to
minimal energy absorption by phonon. This sensitivity to thickness and
efficient energy transfer offers an opportunity to obtain ultrafast on-chip
magnetization dynamics.
