Regensburg 2013 – scientific programme

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MA: Fachverband Magnetismus

MA 43: Magnetization Dynamics II of 3

MA 43.5: Talk

Thursday, March 14, 2013, 16:00–16:15, H22

The lattice response of femtosecond laser excited Nickel investigated by time-resolved electron diffraction — •Carla Streubühr, Ping Zhou, Thorsten Brazda, Frank Meyer-zu Heringdorf, Michael Horn-von Hoegen, Dietrich von der Linde, and Uwe Bovensiepen — Universität Duisburg-Essen

In ultrafast magnetization dynamics of ferromagnets like Ni the lattice response to the femtosecond laser excitation is essential [1]. Here we report on an experimental study of the lattice dynamics driven by laser excitation in 20 nm thick Nickel single-crystalline films using time resolved transmission electron diffraction. The electron diffraction patterns of the freestanding Ni (001) films were recorded as function of delay time between optical pump (hν = 1.5 eV) and electron probe (E_kin = 30 keV).

The integrated intensity of all diffraction spots decreased after the laser excitation. Our analysis indicates that the observed decrease does not scale with the scattering vector which is inconsistent with the Debye-Waller effect resulting from lattice heating. Furthermore, the diffraction intensity drop was proportional to the intensity of the laser pulse rather than the laser fluence. Both observations indicate a higher order lattice excitation by the laser and argue against the excitation by electron-phonon scattering. Possible alternative excitation mechanisms will be discussed.

[1] B. Koopmans et al, Nature Materials 9, 259 (2010)