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MAGNETISME ET TRANSPORT POLARISE EN SPIN DANS DES JONCTIONS TUNNEL MAGNETIQUES. UTILISATION DU TRANSPORT TUNNEL COMME UNE SONDE MICROMAGNETIQUE

Abstract : The spin dependent tunnelling effect in a ferromagnetic /insulator /ferromagnetic structure, which constitutes a magnetic tunnel junction, has regained much interest in the last years since it was demonstrated that the effect also takes place at room temperature. This makes magnetic tunnel junction important potential candidates for the application in micro-electronic devices, such as non-volatile memories, magneto-resistive sensors, etc. In a magnetic tunnel junction the electrons are polarized by the magnetic electrodes. Their tunneling probability across the insulating barrier depends on the characteristics of the insulator as well as the relative orientation of the magnetization of the electrodes. Upon modifying selectively the orientation of the magnetization in one magnetic electrode (soft layer) with respect to the other electrode (hard or reference layer) by application of a field, the resistance of the magnetic tunnel junction varies by more than 20%. A major aspect of this thesis work is the use of an artificial antiferromagnetic (AAF) system as the hard magnetic system in the magnetic tunnel junction. The AAF consists of two magnetic layers (Co and/or CoFe) of different thickness having their magnetization aligned anti-parallel due to the exchange coupling across a non-magnetic spacer layer (Ru). This configuration allows one to obtain a large adjustable magnetic rigidity together with a large thermal stability (>300° C). During this thesis work magnetic tunnel junctions of micronic size were fabricated and the correlation between their magnetic properties and their spin polarized transport properties have been studied in the macroscopic as well as the microscopic regimes. It was found that the spin polarized tunnel transport is extremely sensitive to the fluctuations of the configuration of the magnetization ferromagnetic in the electrodes. This sensitivity makes magnetic tunnel junctions ideal probes to study selectively the field dependent evolution of the domain structure of the ferromagnetic layers which is in direct contact with the insulator.
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Submitted on : Thursday, April 24, 2003 - 10:47:18 AM
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Coriolan Tiusan. MAGNETISME ET TRANSPORT POLARISE EN SPIN DANS DES JONCTIONS TUNNEL MAGNETIQUES. UTILISATION DU TRANSPORT TUNNEL COMME UNE SONDE MICROMAGNETIQUE. Matière Condensée [cond-mat]. Université Louis Pasteur - Strasbourg I, 2000. Français. ⟨tel-00002763⟩

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