Dynamique du retournement de l'aimantation dans les systèmes pour l'enregistrement magnétique

Abstract : In this thesis, magnetisation reversal dynamics in magnetic multilayers has been studied by magneto-optical effects : Kerr effect and x-ray magnetic circular dichroism (XMCD).
Magnetisation reversal of (Pt/Co) multilayers with perpendicular magnetic anisotropy exchange biased with an antiferromagnetic thin film has been studied by time-resolved Kerr microscopy. We have shown that the magnetisation reversal strongly depends on the strength of the exchange bias. Due to magnetic frustrations at the F/AF interface, the nucleation density strongly increases, with respect to that of the free multilayer. Moreover, the nucleation density is larger when the field is applied antiparallel to the exchange bias direction.
Systems with in-plane magnetisation have also been investigated. The magnetisation reversal of magnetic tunnel junctions Co/Al2O3/FeNi has been studied by photo-electron emission microscopy coupled with XMCD. In these systems, we have shown that the topography of the trilayer has a strong impact on the reversal processes. Thanks to the element selectivity of XMCD, the effect of the presence of a domain wall in the cobalt layer on the reversal of the permalloy magnetisation could be studied. We have shown that the stray field of the cobalt domain walls is strong enough to create quasi-walls in the permalloy layer. These quasi-walls locally increase the reversal speed.
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Fabien Romanens. Dynamique du retournement de l'aimantation dans les systèmes pour l'enregistrement magnétique. Matière Condensée [cond-mat]. Université Joseph-Fourier - Grenoble I, 2006. Français. ⟨tel-00127015⟩

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