Electric field-driven magnetocrystalline anisotropy switching of Fe/MgO: Towards full understanding from first principles

Controlling magnetic properties by an external electric field ($E$-field) is a key challenge in modern magnetic physics. Here, we investigate the magnetocrystalline anisotropy (MCA) modification by an $E$-field for thin films of Fe on a MgO substrate from first principles. Calculations were carried out by using the film FLAPW method\footnote{Wimmer, Krakauer, Weinert, and Freeman, PRB {\bf 24}, 864 (1981).} with full optimization by atomic force calculations in which an $E$-field effect is incorporated.\footnote{Nakamura et al., PRL {\bf 102}, 18702 (2009); Weinert et al., J. Phys.: Condens. Matter {\bf 21}, 084201 (2009).} Results predict that the Fe/MgO interface gives rise to a large out-of-plane MCA due to an Fe-O hybridization at the interface and a MCA modification is induced by a change in the $d$-band structures at the Fermi level when an $E$-field is introduced. Importantly, however, the existence of an interfacial iron- oxide layer between the Fe layer and the MgO substrate is found to play a key role in demonstrating an electric field-driven MCA switching, {i.e.,} from out-of-plane MCA to in-plane MCA --- as observed in experiments.\footnote{Shiota et al., Appl. Phys. Express {\bf 2}, 063001 (2009).}