Regensburg 2004 – scientific programme

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MA: Magnetismus

MA 28: Spindynamik / Ummagnetisierungsvorg
änge

MA 28.14: Talk

Thursday, March 11, 2004, 18:30–18:45, H23

Coherent magnetization dynamics on Gd(0001) at 3 THz and its temperature dependence — •Uwe Bovensiepen, Alexey Melnikov, Ilie Radu, Oleg Krupin, Kai Starke, Eckart Matthias, and Martin Wolf — Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin

Resonant absorption of femtosecond laser pulses at the exchange split surface state of Gd(0001) excites coherent optical phonons, which lead to a periodic modulation of the distance between surface and subsurface layer with a frequency of 3 THz [1]. This vibration has been investigated in situ by time-resolved second harmonic (SH) generation on Gd(0001) films grown in ultrahigh vacuum on W(110). The magnetic SH contribution has been extracted by analysis of the SH yield for opposite magnetization directions. As a function of pump-probe delay a modulation of the surface magnetization at 3 THz is detected, which is attributed to a modulation of the exchange coupling due to the lattice vibration. We suggest, that this quasi-instantaneous phonon-magnon coupling is observed near the surface due to a crossing of phonon and magnon dispersion relations. As a function of temperature the lattice and the magnetic oscillation amplitude decrease and vanish near the Curie temperature.

Coherent bulk dynamics is observed by transient reflectivity at 10% higher frequency. These modes are excited due to coupling of the subsurface region to the surface vibration.

[1] A. Melnikov et al.; Phys. Rev. Lett., (2003) in press.