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Du renversement sous champ de l'aimantation d'un nano-plot au deplacement sous courant d'une paroi de domaines dans une nano-piste par microscopie Kerr polaire

Abstract : The goal of this PhD was to study magnetisation dynamics in two perpendicularly magnetised nano-systems; metallic Pt/Co(5 Å)/Pt and the diluted ferromagnetic semiconductor GaMnAs. Magnetisation reversal, under the action of a magnetic field in nano-dots or the spin polarised current induced domain wall motion in a track, has been studied using polar Kerr magneto-optics. Nano-structuration was realised by classical eching to obtain GaMnAs nano-dots and tracks and by an elegant process in the ultrathin cobalt layer case: helium ion irradiation which yields nano-dots in a planar and paramagnetic environment. For these two systems, with different ferromagnetism and anisotropy origins, the lateral confinement implies a transition from a multi-mode reversal to a single-mode reversal. When the nano-dot diameter is close to the exchange length, as is the case in the smallest GaMnAs nano-dot the Néel-Brown reversal allows to interpret experimental results. However, it is shown that the single magnetisation reversal of a 130 nm diameter Pt/Co/Pt nano-disk can not be coherent and individual investigations on these nano-disks as well as a micromagnetic model show that the magnetisation reversal is governed by the nucleation of a droplet at the periphery. In contrast with the metallic case, spin-polarised current induced domain wall motion is easy in the GaMnAs. Measurements performed at a constant effective temperature show that it is mandatory to consider a non-adiabatic spin transfer mechanism.
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Submitted on : Monday, December 7, 2009 - 11:19:39 AM
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Jean-Paul Adam. Du renversement sous champ de l'aimantation d'un nano-plot au deplacement sous courant d'une paroi de domaines dans une nano-piste par microscopie Kerr polaire. Matière Condensée [cond-mat]. Université Paris Sud - Paris XI, 2008. Français. ⟨tel-00439280⟩

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