Giant unilateral electric-field control of magnetic anisotropy in MgO/Rh₂CoSb heterojunctions

A large voltage-controlled magnetic anisotropy (VCMA) effect is highly desirable for applications of voltage-torque magnetic random access memory. In this work, the dependence of magnetic anisotropy (MA) on the electric field in a MgO-based heterojunction consisting of a new Heusler alloy, Rh₂CoSb, is studied using first-principles calculations. We find that the Rh-terminated MgO/Rh₂CoSb heterojunction has a perpendicular MA and a giant VCMA coefficient of 7024 fJ V^-1 m^-1. Furthermore, the VCMA coefficient shows a characteristic of dependence on the electric-field direction. The origins of these behaviors are elucidated by orbital-resolved MA and second-order perturbation theoretical analysis. As the spin-down states of the in-plane orbital, d, are close to the Fermi level, the shift of these states induced by the electric field gives rise to significant changes of magnetic anisotropy energy, which is mainly responsible for the giant VCMA effect.