  We have measured the hot-electron induced demagnetization of a [Co/Pt]2
multilayer in M(x nm)/Cu(100 nm)/[Co(0.6 nm)/Pt(1.1 nm)]2 samples depending on
the nature of the capping layer M and its thickness x. We found out that a Pt
layer is more efficient than [Co/Pt]X, Cu or MgO layers in converting IR photon
pulses into hot-electron pulses at a given laser power. We also found out that
the maximum relative demagnetization amplitude is reached for M(x) = Pt (7 nm).
Our experimental results show qualitative agreement with numerical simulations
based on the superdiffusive spin transport model. We concluded that the maximum
relative demagnetization amplitude, which corresponds to the highest photon
conversion into hot-electrons, is an interplay between the IR penetration depth
and the hot-electron inelastic mean free path within the capping layer.
