Laser-Induced Ultrafast Electron- and Spin-Dynamics in the Electronic Band Structure of Co(001)

Laser-Induced Ultrafast Electron- and Spin-Dynamics in the Electronic Band Structure of Co(001)
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Inhaltsangabe zu "Laser-Induced Ultrafast Electron- and Spin-Dynamics in the Electronic Band Structure of Co(001)"

In the last two decades, ultrafast magnetization dynamics has been the subject of a
large number of experimental and theoretical investigations, however, without establishing
a consistent picture up to now. The objective of the work presented in this
thesis is to provide a new and profound perspective on the underlying mechanisms
by a direct observation of the spin-dynamics in the electronic band structure of 3d
ferromagnets using femtosecond time- and spin-resolved photoelectron spectroscopy
of the full energy range of the valence bands.
For this purpose, a novel experimental setup has been developed and commissioned
that combines a modern, highly ecient spin detector with a state-of-the-art, tabletop
light source creating ultrashort extreme ultraviolet (XUV) pulses by laser-based
high-order harmonic generation (HHG). The light source can be used in two operation
modes, which provide XUV radiation with dierent wavelengths and photon

uxes. Static spin-resolved photoemission spectra of Co(001) lms have been measured
in both operation modes to nd the optimum conditions for time-resolved experiments.
Moreover, vacuum space-charge (VSC) eects within the dense electron
clouds emitted by the femtosecond XUV pulses as well as the Coulomb interaction
between electron clouds generated by XUV probe- and near-infrared (NIR) pumppulses
in a pump-probe experiment have been investigated in detail. The ndings
are used to determine and later minimize the in
uence of VSC on photoemission
results.
The NIR pump-pulses have been employed in time-resolved measurements to trigger
ultrafast demagnetization in Co samples. Using the capabilities of the new
experiment, we monitored the time evolution of the electron-dynamics by measuring
spin-resolved spectra over a broad energy range fully covering the valence bands.
To our knowledge, such measurements have been performed for the rst time. The
experiments lead to novel insights into the evolution of the spin system during an
ultrafast demagnetization process, in particular by showing evidence of spin-mixing
instead of a quenching of the exchange splitting as suggested by the Stoner-model.

Buchdetails

Aktuelle Ausgabe
ISBN:9783958061682
Sprache:Englisch
Ausgabe:Flexibler Einband
Umfang:0 Seiten
Verlag:Forschungszentrum Jülich
Erscheinungsdatum:27.09.2016

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