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Renversement d'aimantation dans des nanostructures par propagation de parois de domaines sous champ magnétique et courant électrique

Abstract : The magnetic domain wall is an essential concept for understanding magnetization reversal in a magnetic film or nanostructure, and can be involved in writing and transmitting information in a nano-device. It was shown theoretically that, in a defect-free magnetic nanostructure, confinement can strongly affect domain wall propagation under a magnetic field and/or a spin-polarized current. This was illustrated by a magneto-optical microscopy study of domain wall propagation in ultrathin Pt/Co/Pt films with perpendicular anisotropy. In these films, nano-tracks were patterned and irradiated at a very low dose with helium ions. These devices were shown to be model systems, ideal for the study of domain wall propagation under field, and appeared as promising systems for studying spin-transfer-induced propagation. However, for the whole range of the current pulses that we injected into these tracks, none of the experimentally observed propagation effects could be ascribed to spin transfer. Following a quantitative evaluation of the current and its polarization in the cobalt layer, this was attributed to an unfavorable balance between Joule heating and spin transfer.

We also built a high resolution polar Kerr magnetometer which uses a highly focused laser beam. Its outstanding resolution, stability and sensitivity are well-adapted for the study of ultrathin magnetic nanostructures with perpendicular anisotropy, down to sub-micron scales.

Finally, we studied magnetic field induced magnetization reversal in a magnetic tunnel junction stack with planar anisotropy, designed for the industrial development of magnetic random access memories. The effect of a high temperature annealing on the magnetic properties of this stack has been tested. Besides, in the soft magnetic layer of the tunnel junction, dipolarly coupled through the tunnel barrier, we evidenced an asymmetry in domain nucleation and domain wall propagation processes depending on the field sweeping direction, which was ascribed to slight inhomogeneities of the dipolar coupling field.
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https://tel.archives-ouvertes.fr/tel-00361478
Contributor : Mathieu Cormier <>
Submitted on : Monday, February 16, 2009 - 3:59:04 PM
Last modification on : Wednesday, October 14, 2020 - 3:56:46 AM
Long-term archiving on: : Friday, October 12, 2012 - 11:50:27 AM

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  • HAL Id : tel-00361478, version 1

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Mathieu Cormier. Renversement d'aimantation dans des nanostructures par propagation de parois de domaines sous champ magnétique et courant électrique. Matière Condensée [cond-mat]. Université Paris Sud - Paris XI, 2008. Français. ⟨tel-00361478⟩

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