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Dynamique d'aimantation de nanostructures magnétiques : Etudes par microscopie Kerr magnéto-optique femtoseconde

Abstract : The thesis deals with experimental studies of the laser induced spin dynamics in magnetic nanostructures. First, we studied the spin dynamics of individual ferromagnetic discs of CoPt3 and permalloy (the diameter vary from 0.25 μm to 30 μm). The experimental set-up consists in time resolved Kerr magneto-optical pump probe measurements in the confocal geometry (the spatial resolution is 300 nm; the temporal resolution is 150 fs). We showed that the spin dynamics depends strongly on the pump intensity particularly the spin-lattice time relaxation and the frequency of magnetization precession. We also studied the spatial expansion of the demagnetisation in a single dot. Additionally, we developed a powerful technique named Magneto-Optical Pump Probe Imaging (MOPPI) used for studying the magnetization switching in CoPt films and in individual dots. We explored the influence of different parameters: the laser intensity, the external static magnetic field, and the crystalline character of the sample (alloy, multilayer) on the magnetization switching. Finally, we performed Magnetic Force Microscopy imaging of the laser induced magnetic domains. We also studied the coherent spin dynamics of magnetic nanoparticles (the average diameter varies from 2 nm to 10 nm) excited with femtosecond laser pulses. The analysis of the three spatial components of the magnetization (polar, longitudinal, and transverse) after the optical excitation (> 120 fs) brings useful information about the ultrafast demagnetization, the gyroscopic motion (precession and damping of the magnetization) that preceeds the super-paramagnetic fluctuations. We explored the influence of the magnetic anisotropy on the ultrafast reorientation of the magnetization and we demonstrated that the damping increases when the diameter of particles decreases.
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https://tel.archives-ouvertes.fr/tel-00198127
Contributor : Abdelghani Laraoui <>
Submitted on : Sunday, December 16, 2007 - 6:44:03 PM
Last modification on : Thursday, April 23, 2020 - 2:26:22 PM
Long-term archiving on: : Monday, April 12, 2010 - 8:06:00 AM

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Abdelghani Laraoui. Dynamique d'aimantation de nanostructures magnétiques : Etudes par microscopie Kerr magnéto-optique femtoseconde. Matière Condensée [cond-mat]. Université Louis Pasteur - Strasbourg I, 2007. Français. ⟨tel-00198127⟩

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