Martin Luther University Halle-Wittenberg

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Prof. Dr. Christian Heiliger

Doctoral Thesis: Elektronentransport durch planare Tunnelkontakte: Eine ab initio Beschreibung (German)

The topic of this thesis is the theoretical description of the electronic transport through planar Fe/MgO/Fe tunnel junctions using an ab initio method. This means that the tunnel magneto resistance effect (TMR) is investigated in the coherent limit of transport. The Landauer formalism is used to calculate the transport properties. This approach is implemented in a Korringa-Kohn-Rostoker (KKR) method based on density functional theory. Consequently, the TMR is analyzed in dependence on different parameters. In particular, the influences of the interface structure, of the barrier thickness, and of the atomic structure of the leads are investigated. It can be demonstrated that the bias voltage dependence of the TMR ratio can be strongly influenced by a possible FeO monolayer. Thereby, positive and negative TMR ratios can be obtained in dependence on the applied bias voltage and on the interface structure. Furthermore, analyzing the states contributing to the current an understanding of the experimentally observed saturation of the TMR ratio for large barrier thicknesses is achieved in the present work. In particular, the complex band structure is of special importance. Another results of this thesis is that even one ferromagnetic monolayer next to the barrier is sufficient to obtain a high TMR ratio.

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