PIER Photon Science Colloquium: From spin-dependent carrier dynamics to femtomagnetism

by Martin Weinelt (Freie Universität Berlin)

Friday, July 1, 2011 from to (Europe/Berlin)
at bldg. 5, auditorium
Demagnetization of ferromagnets can be achieved within a few hundred femtoseconds upon optical excitation. It remains controversial, which microscopic processes are fast enough to provoke this femtomagnetism.
Electrons only undergo a spin flip in the presence of spin-orbit coupling, which becomes significantly enhanced at hybridization points of the valence band-structure. We have identified such spin hot-spots in cobalt by linear magnetic dichroism in spin-resolved two-photon photoemission. For iron we show that magnon emission significantly contributes to the decay of optically excited carriers on the femtosecond timescale.
Time-resolved photoemission with optical laser pulses restricts band mapping to a small k-range. Here we present IR-pump - XUV-probe photoelectron spectroscopy on the ultrafast demagnetization of Gd and Tb. The experiments are the first to be done using a newly developed high-order harmonics beamline. Following excitation by an infrared pulse, TR-ARPES with XUV photons allows us to directly map the transient exchange splitting of the valence bands.