Published in:Jülich : Forschungszentrum Jülich GmbH Zentralbiliothek, Verlag, Schriften des Forschungszentrums Jülich. Reihe Schlüsseltechnologien / Key Technologies 70, VI, 121 S : Ill., graph. Darst (2013). = Universität Duisburg, Diss., 2013
Language:
English
ISBN:
978-3-89336-894-5
ISSN:
1866-1807
Origination:
Footnote:
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Description:
This work explores laser-induced, element-selective, femtosecond spin dynamics in ferromagnetic layered structures. As a model system, interlayer exchange coupled Fe/Ru/Ni layers were investigated in time- and element-selective, magneto-optical measurements at the 3p absorption edges of Fe (54 eV) and Ni (67 eV) in the transversal magneto-optical Kerr effect (T-MOKE) geometry. Spin dynamics was initiated by femtosecond laser excitation with 1.5 eV photon energy. The temporal evolution of magnetization was probed by sub-10 fs pulses of laser high harmonics generated in Ne gas. First, element-selective, temperature-dependent magnetization reversal of the Fe and Ni layers in external magnetic field is traced and the interlayer exchange coupling energy J$_{1}$ is derived for the antiferromagnetically coupled Fe and Ni layers from magnetometer measurements. In the next step, femtosecond dynamics of J$_{1}$ is studied in pump-probe experiments with 1.5 eV optical pump and both 3.0 eV and laser high harmonics probe. In time-resolved measurements of magnetic hysteresis, J$_{1}$ is transiently quenched on the femtosecond timescale by the action of the pump laser, following the demagnetization ofthe Ni layer. Moreover, time- and layer-resolved measurements for parallel and antiparallel magnetization orientation of the Fe and Ni layers and for various pump fluences were carried out. The central and surprising result is, that the (buried) Fe layer is transiently magnetized above its equilibrium magnetization prior to laser excitation $\textit{for parallel orientation}$ and demagnetized $\textit{for antiparallel orientation}$ for a defined pump fluence range. For the highest fluence reached in the experiment, the Fe magnetization is quenched for both parallel and antiparallel orientation, albeit, for antiparallel orientation, the quenching ishigher. Regardless of the relative orientation of the Ni and Fe magnetization and opticalpump fluence, the (top) Ni layer is always demagnetized. The magnetization orientationdependent ...