Berlin 2008 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 72: Symposium: Beyond Optical Wavelengths: Time-Resolved Spectroscopy of Surface Dynamics with EUV and XUV Radiation II (Invited Speakers: Wilfried Wurth, Hermann Dürr, Shik Shin)

O 72.4: Hauptvortrag (ohne Erstattung)

Donnerstag, 28. Februar 2008, 15:15–15:45, HE 101

Ultrafast Magnetization Dynamics Probed by Femtosecond X-Ray Spectroscopy — •Hermann A. Dürr — BESSY GmbH, Albert-Einstein-Str. 15, 12489 Berlin, Germany.

When the electronic system of a solid is rapidly heated by absorbing a femtosecond optical laser pulse it takes time to re-establish thermal equilibrium. This timescale is ultimately determined by energy transfer from the electronic system to the lattice. For ferromagnets this process can also lead to an ultrafast quenching of the ferromagnetic order. Angular momentum conservation dictates that an exchange of spin angular momentum with a reservoir such as the lattice should occur. So far real time studies of these processes were limited to the use of femtosecond laser pump-probe spectroscopy [1]. We show that an efficient novel channel for angular momentum dissipation to the lattice can be opened by fs laser excitation of a ferromagnet [2]. The quenching of spin angular momentum and its transfer to the lattice with a time constant of 120 fs is determined unambiguously with x-ray magnetic circular dichroism by separating spin and orbital contributions to the magnetization. Fs time-resolved x-ray absorption spectroscopy shows an unexpected increase in valence electron localization during the first 120 fs possibly providing the driving force behind fs spin-lattice relaxation.

[1] E. Beaurepaire, et al., Phys. Rev. Lett. 76, 4250 (1996).

[2] C. Stamm, et al., Nature Materials 6, 740 (2007).