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MA: Fachverband Magnetismus
MA 14: Magnetization Dynamics II
MA 14.2: Talk
Monday, March 14, 2011, 17:15–17:30, HSZ 403
Influence of equilibrium temperature on the femtosecond magnetization dynamics of Gd — •Muhammad Sultan1,2, Alexey Melnikov2, and Uwe Bovensiepen1 — 1Fakultät für Physik, Uni. Duisburg-Essen — 2Fachbereich Physik, Freie Uni. Berlin
Understanding the demagnetization of solids after femtosecond laser excitation requires the knowledge of the involved processes and their time scales. Previously we found by fs time resolved X-ray magnetic circular dichroism that Gd exhibits at an equilibrium temperature To=120K a faster and a slower demagnetization with characteristic time scales τf=0.75 ps and τs=40 ps, respectively [1]. In this study we focus on the question how To affects laser induced demagnetization. We employed the magneto-optical Kerr effect to investigate the temperature dependence of both demagnetization time scales. We find that the demagnetization evolves slower in time with increasing To for both processes. However, in detail they show different temperature dependence. τf increases linearly with temperature and exhibits a larger dτf/dTo for To>170K, τf enhanced to double between 50 and 280 K. Remarkably, τs increases by a factor of five in the same temperature interval and follows a continuous change that suggests a divergence at the Curie temperature Tc. These findings demonstrate that thermal spin fluctuations influence the laser induced demagnetization and tend to inhibit the demagnetization in line with an increase of spin fluctuation times if a ferromagnet reaches Tc under equilibrium conditions.
[1] Wietstruk et al, submitted arxiv.org/abs/1010.1374