Colossal electric field control of magnetic anisotropy at ferromagnetic interfaces induced by iridium overlayer

Voltage-induced magnetization switching can lead to a new paradigm enabling ultralow-power and high density instant-on nonvolatile magnetoelectric random access memory (MeRAM) devices. Two major challenges for future MeRAM devices are to achieve large perpendicular magnetic anisotropy (PMA) and high voltage-controlled magnetic anisotropy (VCMA) coefficient of heavy-metal/ferromagnet/insulator heterostructures (HM/FM/I). Employing ab initio electronic structure calculations we have investigated the effect of epitaxial strain and thickness of both FeCo and Ir layers as design parameters to optimize the PMA and VCMA of Ir/FeCo/MgO. We predict that the Ir cap layer can induce both large PMA and colossal VCMA efficiency which depend on the strain. More importantly, we predict that a single Ir cap monolayer gives rise to a VCMA efficiency one order of magnitude higher than that of thicker Ir layers. The underlying mechanism is the synergistic effects of the emergence of Ir local moments, the large Ir spin-orbit coupling (SOC), and the large modulation of the magnetic anisotropy at the Ir/vacuum interface. These results provide useful guiding rules in the design of the next generation of high performance MeRAM memory devices.