  We investigated the effect of an electric field on the interface magnetic
anisotropy of a thin MgO/Fe/MgO layer using density functional theory. The
perpendicular magnetic anisotropy energy (MAE) increases not only under
electron depletion but also under some electron accumulation conditions,
showing a strong correlation with the number of electrons on the interface Fe
atom. The reverse variation in the MAE under the electric field is ascribed to
novel features on the charged interface, such as electron leakage. We discuss
the origin of the variation in terms of the electronic structures.
