We investigate the fluence-dependent dynamics of the exchange-split 5d6s
valence bands of Gd metal after femtosecond, near-infrared (IR) laser
excitation. Time- and angle-resolved photoelectron spectroscopy (tr-ARPES)
with extreme ultraviolet (XUV) probe pulses is used to simultaneously map the
transient binding energies of the minority and majority spin valence bands.
The decay constant of the exchange splitting increases with fluence. This
reflects the slower response of the occupied majority-spin component, which we
attribute to Elliot–Yafet spin-flip scattering in accordance with the
microscopic three-temperature model (M3TM). In contrast, the time constant of
the partly unoccupied minority-spin band stays unaffected by a change in pump
fluence. Here, we introduce as an alternative to superdiffusive spin transport
exchange scattering, which is an ultrafast electronic mechanism explaining the
observed dynamics. Exchange scattering can reduce the spin polarization in the
partially unoccupied minority-spin band and thus its energetic position
without effective demagnetization