Martin Luther University Halle-Wittenberg

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Dr. Peter Bose

Doctoral Thesis: Influence of the interface structure on the electronic transport in planar tunnel junctions: A first-principles investigation

Previous theoretical investigations on the tunnel magnetoresistance in planar tunnel junctions have found that the electronic transport properties are significantly affected by the properties of the interfaces. In this thesis, this important issue is studied in more depth. The ab initio computations for ballistic transport rely on the Landauer-Büttiker approach, as formulated in multiple-scattering theory (layer Korringa-Kohn-Rostoker method). The addressed issues can be cast into two categories: substitutional disorder and the effect of magnetic interlayers which are embedded in Fe/MgO/Fe tunnel junctions. Experimentally it was found that the interfaces in Fe/MgO/Fe junctions can be partially oxidized, leading to substitutionally disordered FeO_{c} interface layers. These have been treated within a supercell approach. The main result is that the tunneling magnetoresistance ratio (TMR) is strongly reduced, by 80 %, for an oxygen concentration of c = 4 %, as compared to the ideal junction (c = 0). The other focus in the thesis is to answer the question whether the embedding of magnetic interlayers (Mn, Cr, Co) allows to increase and to tune the TMR ratio.

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Diploma Thesis: Tunneling Within the Nearly-Free-Electron Model

Spin-dependent ballistic transport through a tunnel barrier is treated within the one-dimensional nearly-free-electron model. The comparison with free electrons reveals significant effects of band gaps, in particular in the bias dependence.

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