Renversement d' aimantation par injection d' un courant polarise en spin

Abstract : This thesis is dedicated to the experimental study of the spin transfer effect. This mecanism was introduced theoratically in 1996 by J. Slonczewski. It allows to switch the magnetization of a ferromagnet without any applied field, only by injection of a spin polarized current and subsequent transfer of spin towards the ferromagnet. High current densities (about 107 A.cm-2), are required to reverse a magnetization by spin tranfer. Experimental evidence of the spin transfer effect can then only be reached by processing nanostructures. We have followed two different paths in order to caracterize this new spin transfer effect between a current and a magnetization. On one hand, similarly to the very first experimental results obtained at Cornell University in 2000, we have studied the effect in submicron Co/Cu/Co magnetic pillars. We have clearly evidenced the magnetization reversal by a spin polarized current at zero field. We have then focused on the field dependence of the critical curents. This study has allowed us to draw, experimentally as well as theoratically, the field vs. current phase diagram, bringing out important informations concerning the microscopic mecanisms at the origin of the magnetization reversal by spin injection. The second part of my thesis focuses on the case of Co/Cu/NiFe spin-valve stripes, in which the magnetization reversal occurs by magnetic domain wall (DW) motion. We have shown that this motion can be induced by transfer of spin from a spin-polarized current. When the magnetic field is close to zero, a DW can be displaced between pinning centers, using only current injection. In agreement with the Berger model, the motion occurs in different directions when the sign of the current is changed. The involved current densities in order to achieve DW motion are of the order of a few 106 A/cm², one order of magnitude lower than the currents required to reverse the magnetization in pillar-like structures. This measurements evidence for the first time, directly and in real-time, DW displacement by spin transfer in magnetic nanostructures.
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Submitted on : Wednesday, December 10, 2003 - 12:12:06 PM
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Julie Grollier. Renversement d' aimantation par injection d' un courant polarise en spin. Matière Condensée [cond-mat]. Université Pierre et Marie Curie - Paris VI, 2003. Français. ⟨tel-00003941⟩

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