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O: Oberflächenphysik

O 25: Zeitaufgelöste Spektroskopie II

O 25.5: Vortrag

Samstag, 5. März 2005, 16:00–16:15, TU EB420

Ultrafast dynamics of the exchange split surface state of Gd(0001)/W(110) — •Martin Lisowski, Panagiotis Loukakos, Uwe Bovensiepen und Martin Wolf — Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin

Gadolinium is a model system for ferromagnetic materials where the exchange interaction of localized magnetic moments is mediated via spin-polarization of the conduction band electrons (RKKY interaction). An interesting question is, whether it is possible to demagnetize such a ferromagnet on a femto-second time scale by disturbing the conduction band electrons. We use time resolved photoelectron spectroscopy to investigate the dynamics of the Gd(0001)/W(110) surface upon excitation with an optical pump pulse. The use of a probe photon energy above the work function of Gd allows us to directly measure the transient electron temperature as well as the occupied and unoccupied part of the exchange split surface state, which serves as a probe for magnetism. We observe a sub pico-second reduction of the SS binding energy. Comparison with a two-temperature model simulation shows that the decrease in binding energy is initially faster than the increase in lattice temperature, excluding a simple lattice heating effect as explanation. A damped oscillation of 2.8 THz frequency and 1 ps damping time is superimposed on the binding energy shift and is attributed to a coherent LO phonon-magnon mode.