Berlin 2008 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 52: Time-Resolved Spectroscopy III
O 52.3: Vortrag
Mittwoch, 27. Februar 2008, 15:45–16:00, MA 042
Coherent dynamics at Gd(0001) and Tb(0001) surfaces: magnon-enhanced damping of optical phonons — •Alexey Melnikov1, Alexey Povolotskiy2, and Uwe Bovensiepen1 — 1Freie Universität Berlin, Institut für Experimentalphysik, Arnimallee 14, D-14195 Berlin, Germany — 2St. Petersburg State University, Laser Research Institute, St. Petersburg, 198504 Russia
Coherent lattice and spin dynamics were studied at the Gd(0001) surface by time-resolved second harmonic generation [1]. To understand the elementary processes responsible for optical excitation and damping of coherent phonons (CP) and magnons (CM), we perform temperature-dependent studies in Gd and Tb. With lowering the temperature T from the Curie point TC to 40K amplitudes of CP and CM increase by more than an order following the increase of spin ordering and showing an essentially "magnetic" nature of the excitation. The CP damping rate Γ increases linearly with the temperature in transition metals, which is attributed to anharmonic phonon-phonon scattering [2]. In Gd we observe a monotonous increase of Γ (T) at T<TC but near TC it reduces significantly. We explain this by phonon-magnon scattering contributing to Γ at T<TC. This contribution scales with the magnetoelastic constant mediated by the spin-orbit interaction. This conclusion is confirmed by Γ (T) measured in Tb (L=3), where the spin-lattice coupling is much larger than in Gd (L=0): the phonon-magnon contribution to Γ (T) is found to be 6 times larger than in Gd.
[1] A. Melnikov et al., Phys. Rev. Lett. 91, 277403 (2003).
[2] M. Hase et al., Phys. Rev. B 71, 184301 (2005).