Damping of coherent optical phonons is investigated by femtosecond time-resolved second harmonic generation at Gd(0001) and Tb(0001) surfaces. At low temperature the damping rate increases monotonously with temperature. This changes close to the Curie point where the damping rate is strongly reduced. We explain this behavior by phonon-magnon scattering proven by a six times larger effect for Tb than for Gd. Consideration of elastic processes and inelastic phonon-phonon scattering shows that magnon-mediated damping is dominant up to the Curie temperature.
The original publication is available at www.springerlink.com by link DOI: 10.1103/PhysRevLett.100.247401