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Analyse du transport dans les jonctions tunnel magnétiques épitaxiées à barrière de MgO(001) par manipulation des interfaces, de la barrière et des électrodes

Abstract : Epitaxial magnetic tunnel junctions are model systems in order to test the spin polarized tunnel effect theory. MgO(001) based junctions are thus subject of many studies. Some of them experimentally established the existence of coherent tunnelling involving the symmetry of Bloch states. However quantitatively, characteristics of real junctions strongly deviate from predictions. The role of imperfections in the barrier and at the interfaces is suspected but the current knowledge of dominant mechanisms is still limited. This thesis experiments aim at identifying and controlling several properties of the interfaces, of the barrier and of the electrodes which influence tunnelling. We study the consequences of an excess of oxygen at the Fe/MgO interface in Fe/MgO/Fe(001) junctions. Preparing a model Fe/p(1×1) O/MgO/Fe(001) stacking allows us to confirm some expected effects, namely the appearance of an additionnal potential barrier at the interface for states with Δ1 symmetry. However, and unexpectedly, the magnetoresistance little depends on the presence of oxygen. On the other hand, it is very sensitive to the crystallographic quality of interfaces. We show evidence for the detrimental influence of disorder and of the misfit between the MgO barrier and the supporting electrode. Using Fe V alloys with variable composition allows us to reduce the misfit and the dislocations density, which in turn induces a great enhancement of the magnetoresistance. We finally investigate how the electronic structures of Fe Co and Fe V alloys express themselves in tunnelling. In addition, we probe by spin resolved photoemission the Δ bands and interfacial resonance states of free and MgO covered (001) surfaces.
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Submitted on : Monday, February 15, 2010 - 10:36:26 AM
Last modification on : Thursday, February 25, 2021 - 11:04:22 AM
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  • HAL Id : tel-01748291, version 2

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Frédéric Bonell. Analyse du transport dans les jonctions tunnel magnétiques épitaxiées à barrière de MgO(001) par manipulation des interfaces, de la barrière et des électrodes. Matière Condensée [cond-mat]. Université Henri Poincaré - Nancy 1, 2009. Français. ⟨NNT : 2009NAN10098⟩. ⟨tel-01748291v2⟩

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