  A theoretical calculation is performed for the ultrafast spin dynamics in
nickel using an exact diagonalization method. The present theory mainly focuses
on a situation where the intrinsic charge and spin dynamics is probed by the
nonlinear (magneto-)optical responses on the femtosecond time scale, i.e.
optical second harmonic generation (SHG) and the nonlinear magneto-optical Kerr
effect (NOLIMOKE). It is found that the ultrafast charge and spin dynamics are
observable on the time scale of 10 fs. The charge dynamics proceeds ahead of
the spin dynamics, which indicates the existence of a spin memory time. The
fast decay results from the loss of coherence in the initial excited state.
Both the material specific and experimental parameters affect the dynamics. We
find that the increase of exchange interaction mainly accelerates the spin
dynamics rather than the charge dynamics. A reduction of the hopping integrals,
such as present at interfaces, slows down the spin dynamics significantly.
Besides, it is found that a spectrally broad excitation yields the intrinsic
speed limit of the charge (SHG) and spin dynamics (NOLIMOKE) while a narrower
width prolongs the dynamics. This magnetic interface dynamics then should
become accessible to state of art time resolved nonlinear-optical experiments.
