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Coupled electron-spin-lattice dynamics in rare earth materials investigated by femtosecond laser-synchrotron experiments
by Uwe Bovensiepen(University Duisburg-Essen, Faculty of Physics, Duisburg, Germany)
Mardi 26 avril à 11h00, Grand Amphi SOLEIL
Dynamics in the optically excited state proceeds in the ultrafast regime, i.e. on sub-picosecond timescales. Pump-probe experiments are carried out directly in the time domain and allow an analysis of the interaction between electronic, phononic, and magnetic excitations. In this talk recent work on Tb and Gd will be discussed.
In the laboratory a variety of experiments using time-resolved photoelectron spectroscopy and non-linear magneto-optics have been carried out and led to a detailed insight into excitation and relaxation of the optically excited state at Gd(0001) and Tb(0001) surfaces [1]. Using the femtosecond slicing facility at BESSY II time-resolved x-ray magnetic circular dichroism (tr-XMCD) studies have been performed on polycrystalline Gd and Tb films.
This approach provides a reliable observable of the transient ferromagnetic state, which was controversially discussed on the basis of time-resolved magneto-optical experiments. In a very recent tr-XMCD study we show, that Tb and Gd demagnetize after optical excitation in a two step manner [2]. The slower timescale (Gd 40 ps, Tb 8 ps) is attributed to spin-lattice coupling and a quasi-equilibrium process. The ultrafast process (750 fs for both Gd and Tb) is active while hot electrons decay and is therefore linked to the non-equilibrium regime.
[1] U. Bovensiepen, J. Phys.: Cond. Matter 19, 083201 (2007).
[2] M. Wietstruk, A. Melnikov, C. Stamm, T. Kachel, N. Pontius, M. Sultan, C. Gahl, M. Weinelt, H.A. Dürr, U. Bovensiepen, Phys. Rev. Lett. (2011), in press; available oni arxive.org