  Electronic excitations in a ferromagnet can trigger ultrafast spin dynamics
with potential applications in a speed increase in magnetic recording. The
project investigates ultrafast magnetization dynamics, which is driven in
metallic layers by ballistic hot electrons. In a ferromagnet these electrons
induce a change in the absolute value of the magnetization M through
spin-dependent scattering. If the electrons are spin-polarized, scattering at
the interface of a noble metal and a ferromagnet results in spin-transfer
torque and hence modifies the direction of M. To reveal the underlying
mechanisms, we study model systems, which are realized by layers of Au with its
large ballistic mean free path and Fe as an itinerant ferromagnet. We aim at
understanding ultrafast demagnetization and femtosecond all-optical generation
of spin transfer torque effects (excitation of hot electrons with a femtosecond
laser). The launched dynamics are probed by magneto-optics in a time-resolved
experiment.
