Berlin 2008 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 72: Symposium: Beyond Optical Wavelengths: Time-Resolved Spectroscopy of Surface Dynamics with EUV and XUV Radiation II (Invited Speakers: Wilfried Wurth, Hermann Dürr, Shik Shin)
O 72.5: Vortrag
Donnerstag, 28. Februar 2008, 15:45–16:00, HE 101
Non-equilibrium spin-dynamics of Gd(0001) studied by magnetic linear dichroism in 4f core-level photoemission — •Alexey Melnikov1, Helena Prima-Garcia2, Martin Lisowski1, Tanja Gießel2, Ramona Weber2, Roland Schmidt2, Cornelius Gahl2, Nadezhda Bulgakova3, Uwe Bovensiepen1, and Martin Weinelt1,2 — 1Freie Universität Berlin, Fachb. Physik, Arnimallee 14, 14195 Berlin, Germany — 2Max-Born-Institut, Max-Born-Straße 2 A, 12489 Berlin, Germany — 3Institute of Thermophysics SB RAS, pr. Lavrentiev 1, 630090 Novosibirsk, Russia
The magnetic linear dichroism of the Gd 4f core-level is studied in a time-resolved photoemission (PE) experiment at BESSY II employing 1.55eV, 100fs laser pump and 60eV, 50ps synchrotron-radiation probe-pulses. We define the dichroic contrast Δ M(T) at temperature T averaging the difference of PE spectra for opposite magnetization direction. Δ M(T) follows the spontaneous magnetization, vanishes at the Curie temperature TC, and can therefore be used to map the order of the 4f spin-system. The latter is reduced upon optical excitation of the 5d6s valence electrons. Remarkably, Δ M(T) remains at 80% of the equilibrium value while the lattice temperature increases up to TC. A simulation of Δ M(T(τ)) by a quasi-equilibrium model predicts an at least two times larger reduction of Δ M(T) for delays τ below 100 ps. We conclude that at these early times equilibration between lattice and 4f spin subsystems has not been established. This reveals principal differences to the spin dynamics in itinerant ferromagnets, where the valence electrons excited by the laser also carry the magnetic moment.