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Le déplacement asymétrique des parois de domaine magnétiques : ses causes et ses effets

Abstract : The study of the current-induced magnetic domain walls motion has attracted a lot of interest since the report of their large velocities of motion in thin layers with structural inversion asymmetry (SIA). This interest comes from their high potential for low power consumption functionalities in cache and main memories applications. The SIA induces two mechanisms whose combined action allows to drive efficiently the domain walls. The two mechanisms are the chiral energy term, called the Dzyaloshinskii-Moriya interaction (DMI), and the spin-orbit torques (SOT). This model is still incomplete since it does not explain several experimental results. In addition, a chiral dissipation term called the chiral damping, also induced by SIA, has recently been proposed. However, its effect on current-induced domain wall motion has not been studied.The objective of this work was to bring a more detailed understanding of the interactions involved in the domain wall motion. To that end, I have studied the domain wall motion in a non-collinear geometry with respect to the current, in materials with different SIA (Pt/Co/Pt and Pt/Co/AlOx). This motion has been found to be asymmetric. It illustrates the interplay between chiral energy and chiral dissipation in current-induced domain wall motion in weak SIA materials. In large SIA materials, the DMI and SOT model, even in the flow regime of motion, cannot explain this asymmetry. I have also evidenced that the asymmetric non-collinear domain wall motion induces a well-defined deflection of the skyrmion bubbles. This is the first observation of the extrinsic skyrmion Hall effect.The results of this thesis contribute to the understanding of the physical mechanisms behind domain wall and skyrmion motion in ultrathin layers by evidencing supplementary effects from SIA.
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Mohamed Ali Nsibi. Le déplacement asymétrique des parois de domaine magnétiques : ses causes et ses effets. Mesoscopic Systems and Quantum Hall Effect [cond-mat.mes-hall]. Université Grenoble Alpes, 2019. English. ⟨NNT : 2019GREAY047⟩. ⟨tel-02512896⟩

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