Voltage-Controlled Magnetic Anisotropy in Heterostructures with Atomically Thin Heavy Metals

The demand for higher-density, higher-speed, and more energy-efficient magnetoelectric RAM (MeRAM) requires the search of promising materials and magnetic-tunnel-junction stacks with voltage-controlled magnetic anisotropy (VCMA) efficiency greater than the 1000 fJ/(Vm). Using first-principles electronic structure calculations, we propose a double-barrier ferromagnetic heterostructure with an atomically thin late transition metal X (Rh, Ir, Pt), which exhibits both giant perpendicular magnetic anisotropy (PMA) and VCMA efficiency, where the former (latter) is 1 (1 to 2) order of magnitude higher than the values reported to date. We demonstrate that the dominant contribution to both the PMA and VCMA arises from the late heavy metal X due to the large biaxial tensile strain-induced magnetism in X. Furthermore, we predict a sign reversal of the VCMA efficiency from the Ir- to the Pt-monolayer cap. We elucidate that the underlying mechanism is the electric-field-induced energy shift of the spin-polarized d(z2)-derived projected states on the X layer. These findings provide useful guiding rules in exploiting the large spin-orbit coupling and biaxial tensile strain-induced magnetism in the late 5d-transition metals for the design of the next generation of ultra-low energy MeRAM devices.