The prediction and experimental demonstration of a very large magnetoresistance in Fe/MgO/Fe tunnel junctions have led to intense study of related systems in the last decade. In the present paper, we concentrate on the role of interface coordination, Fe thickness, and magnetization in the MgO/Fe/MgO mirror. By first-principles analysis, it is shown that the iron magnetic moment can rise up to 4 μ${}_{\mathrm{B}}$, accounting for observed deviation of the Fe atoms in the vicinity of MgO interfaces. The origin is attributed to site preference predicted by our calculations, namely, that, unlike the case of Fe atoms in the monolayer range sitting just above the oxygen atoms of the MgO(001) substrate, the charge transfer induced by the O $p$-$d$ Fe interaction leads to a structural distortion that stabilizes the Mg at the very first deposition stages of the capping layer, facing Fe sites.

• Received 23 September 2011

DOI:https://doi.org/10.1103/PhysRevB.85.064417