First-Principles Study of Electric Field Effects on Magnetic Anisotropy in MgO/TM/Au (TM = Fe, Co) Systems

We study the electric field (EF) effects on the magnetic anisotropy in the MgO/TM/Au (TM = Fe, Co) systems with (001) and (111) orientations using relativistic first-principles calculations based on the density functional theory. We find that the perpendicular magnetic anisotropy of the MgO/TM/Au(001) system is enhanced by the EF that decreases the number of electrons in the system. The magnetic anisotropy energy (MAE) and its EF dependence of the MgO/Fe/Au(001) system is found to be in a semi-quantitative agreement with the experimental results with successful reproduction of the sign of the measured EF dependence. Furthermore, the EF dependence of the MAE of the MgO/Co/Au(001) system is found to be very large due to the structural relaxation of the Co--O interatomic distance and the decrease in the number of electrons in the Co atom caused by the EF. This result is attributed to the general trend that the perpendicular magnetic anisotropy of the Co layer is affected significantly when in contact with an inert layer at an interlayer distance of about 2 $Å$. On the contrary, we find that the MgO/TM/Au(111) system shows almost no EF dependence of the MAE. This result is attributed to the existence of a strong TM--O covalent bond associated with the oxidation of the TM atom by the O atom.