Abstract
Magnetic tunnel junctions with amorphous ferromagnetic CoFeB electrodes and a crystalline MgO Barrier show a very high tunnel magnetoresistance (TMR). In epitaxial systems of Fe/MgO/Fe(001) these high TMR values can be explained by an effective coupling of electronic states of the electrodes to evanescent states of the barrier and a spin-filter effect of the MgO barrier. It is known from theoretical calculations that for high TMR values only a few monolayers of crystalline iron at the interface to the barrier are sufficient. The quantitative correlation between electric transport and crystalline order of the ferromagnetic electrodes near the interface to the MgO barrier was investigated in this thesis experimentally. For this purpose structured tunnel junctions were characterized by transport measurements and then prepared for high resolution transmission electron microscopy (HRTEM) by a focussed ion beam. In order to quantify the structural order with HRTEM the intensity distribution of averaged experimental images was compared to simulated images. To generate the simulated images a three-dimensional distribution function was used to describe the amorphous electrode near the interface.
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