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MA: Fachverband Magnetismus

MA 22: Magnetization Dynamics I

MA 22.9: Vortrag

Mittwoch, 2. April 2014, 11:45–12:00, HSZ 401

Thickness dependent ultrafast magnetization dynamics in Co/Cu(100) films — •Jens Wieczorek, Nicolas Bergeard, Andrea Eschenlohr, Alexander Tarasevitch, Boris Weidtmann, Andreas Duvenbeck, and Uwe Bovensiepen — Universität Duisburg-Essen, Fakultät für Physik, Germany

To disentangle the local and non-local contributions in femtosecond laser induced demagnetization [1,2,3], we measure the variation of the magneto optical Kerr rotation and ellipticity of Co/Cu(100) films at thicknesses 2 nm < d < 20 nm. We find an increasing quenching of the magnetization and a shift of the time delay of maximum demagnetization to longer delay times with increasing film thickness. Both effects result from a competition between light absorption in cobalt and energy transport to copper. Due to the high thermal conductivity copper acts in our investigated sample as an energy sink. For thicker films the transport to the substrate is decreased due to lower heat conductivity in cobalt and the energy remains longer in Co. This results in a higher excess electron energy density and a reduced cooling, so that the sample can demagnetize longer and stronger. This behavior is also seen in three temperature model [3] simulations, which include different heat conductivity in Co and the Cu substrate. This shows the importance of energy transport to a conducting substrate in magnetization dynamics. We acknowledge support by the DFG through SFB616 and the Mercator Research Center Ruhr through Projekt 2011-0003. [1]Battiato et al., PRL 105, 027203 (2010); [2]Melnikov et al., PRL 107, 076601 (2011); [3]Koopmans et al., Nat. Mat. 9, 259 (2010).