Dresden 2014 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 22: Magnetization Dynamics I
MA 22.3: Vortrag
Mittwoch, 2. April 2014, 10:00–10:15, HSZ 401
The role of spin-lattice coupling in the ultrafast demagnetization of GdTb alloys — •Andrea Eschenlohr1,2, Muhammad Sultan1, Alexey Melnikov3, Nicolas Bergeard1, Jens Wieczorek1, Torsten Kachel2, Christian Stamm2, and Uwe Bovensiepen1 — 1Universität Duisburg-Essen — 2Helmholtz Zentrum Berlin — 3Fritz-Haber-Institut der MPG, Berlin
Gd1−xTbx shows a two-step demagnetization after femtosecond (fs) laser excitation typical for rare earths [Wietstruk et al., PRL 106, 127401 (2011)]. With fs time-resolved magneto-optical Kerr effect measurements we see that the time constant τ1 of the first step is not correlated to x, while the rate γ2 = 1/τ2 of the second step increases linearly with x. We therefore assign the first demagnetization step to the non-equilibrium dynamics of the 5d electrons, while the second step, which occurs under quasi-equilibrium conditions after electron-phonon equilibration, is dominated by the strong spin-lattice coupling of Tb given by the spin-orbit coupling of its 4f shell with L=3. Complementary fs time-resolved x-ray magnetic circular dichroism measurements show a shared τ2 of Gd and Tb in Gd0.6Tb0.4, but a transient difference in their magnitude of demagnetization. We attribute this to an increased spin-lattice coupling of Gd in Gd0.6Tb0.4, compared to pure Gd, via 5d-5d interatomic exchange coupling to neighboring Tb atoms. This coupling however has a limited efficiency, which explains the transient difference.
We acknowledge funding from BMBF Grant 05K10PG2 Femtospex and the DAAD-HEC Pakistan.