Epitaxial magnetic tunnel junctions Fe/MgO/Fe(001) exhibit noteworthy behaviors for both small and large MgO thicknesses. In the first case, a strong antiferromagnetic interaction between Fe layers is observed, whereas symmetry filtering effects occur for large barriers, leading to high TMR values. The aim of the experiments performed during this thesis is to study and link these two behaviors. We consider the effect of a modulation of electrodes and/or interfaces crystalline structure on spin-polarized transport, by means of temperature and voltage analyses. In this framework, we focus on three systems: Fe/MgO(001)/CoFeB hybrid junctions, where the CoFeB electrode is grown by sputtering and in situ recrystallized, textured Fe/MgO/Fe(001) junctions, and finally single crystalline (001)Fe/MgO/Fe junctions with an artificial roughness at the electrode/barrier interface. The antiferromagnetic coupling in epitaxial Fe/MgO/Fe(001) systems with a thin MgO barrier is studied by magnetometry measurements in the [5 K; 500 K] range. We also consider the effect of structural and/or chemical changes resulting from a controlled roughness or a contamination on the coupling. The most interesting results of this thesis are obtained with the introduction of an artificial roughness at the Fe/MgO interface. Unexpectedly, this controlled disorder can improve the magnetoresistance effect or the coupling intensity. In both cases, this result is attributed to a Fe-O hybridization, which emphasizes the role of oxygen in MgO based magnetic tunnel junctions for both behaviors associated with extremely thin or thick barriers.
