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Etude de la dynamique hyperfréquence de l'aimantation de nanostructures magnétiques à anisotropie perpendiculaire

Abstract : This work is devoted to the theoretical and the experimental study of the fast magnetization dynamics in high perpendicular anisotropy (Co3Å/Pt6Å)6 nanostructures. I proposed to assist the magnetization switching by an in-plane exchange bias field. An analytical model was developed in the macrospin approximation. This exchange bias field reduces significantly the needed amplitude of the reversal pulse field both if the field is parallel to the exchange bias field or if it is out of the sample plane. In this latter case, direct overwrite is possible and the decrease in the reversal field can be used to increase the magnetic recording areal density in hard discs by 24%, by resorting to higher anisotropy materials. The experimental aspect contains two parts. The first part concerns the design, the microfabrication and the sample characterization. After the definition of the high frequency circuits, four technological processes for sample fabrication have been tested and compared. The microcircuits incorporate localized source of magnetic field that has the shape of either a microcoil or a coplanar waveguide. Their bandwidths vary between 14 GHz and 20 GHz. The typical generated magnetic fields by the microcoil and the coplanar waveguide are respectively 1.9 Oe/mA and 1.3 Oe/mA. Time-resolved measurements using extraordinary Hall effect were made to probe the magnetization precession induced by the in-plane pulse field. The high DC resistance of the Co/Pt multilayer rendered the detection of this signal difficult. Quasi-static magnetization switching measurements using single/train of pulses of nanosecond durations assisted by an out-of-plane static field have been done. The pulse likely induced nucleation of reverse domains in the cross. As an example, we demonstrated that pulse field of 32 mT and 10 ns can switch the magnetization in most of a 500´500 nm2 nanostructure if it is assisted by an out-of-plane static field of 22 mT.
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Contributor : Mohamed Belmeguenai <>
Submitted on : Tuesday, May 31, 2005 - 10:53:19 AM
Last modification on : Wednesday, October 14, 2020 - 3:57:11 AM
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Mohamed Belmeguenai. Etude de la dynamique hyperfréquence de l'aimantation de nanostructures magnétiques à anisotropie perpendiculaire. Matière Condensée [cond-mat]. Université Paris Sud - Paris XI, 2004. Français. ⟨tel-00009106⟩

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