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SYDU: Dynamik von Ummagnetisierungsvorgängen

SYDU V: HV V

SYDU V.1: Invited Talk

Thursday, March 29, 2001, 11:45–12:15, S5.2

Transient magneto-optics versus femtosecond spin dynamics in ferromagnetic metals — •Bert Koopmans — Department of Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands

Recently, several groups reported on the almost instantaneous quenching (<100 fs) of the magneto-optical (MO) contrast in ferromagnetic transition metals after excitation by an intense laser pulse. In this presentation it will be shown that a separation of genuine magnetic effects and MO artifacts, such as state filling, is possible by careful measuring the magnetic field and temperature dependence of the transient MO response. Moreover, important information can be obtained from explicitly recording the MO rotation and ellipticity, as well as varying the chirp on the laser pulses. Experiments on epitaxial (111) and (001) oriented Cu/Ni/Cu wedges and ion-irradiated Pt/Co/Pt will be presented. During the first hundreds of femtoseconds after excitation, the transient MO response is dominated by No-dqinstantaneousNo-dq state filling effects. The true magnetization relaxation is found to take 0.3 to 0.5 ps for Ni and Co, respectively. The demagnetization times are in surprising agreement with the energy equilibration times of the electron- and phonon-system measured in these materials. These results provide a challenging input to the development of a theoretical description of ultrafast spin dynamics in transition metals.