Low current writing perpendicular magnetic random access memory with high thermal stability

Abstract

Spin reorientation temperature (TSR) is investigated in both layers, including Co/Ni multilayer and composite layer consisting of Co/Pt multilayer with CoFeB layer. The TSR of both layers can be adjusted in a wide range, and the low TSR is obtained in both layers. It is also suggested a writing method based on spin transfer torque (STT) with spin reorientation, for low current writing perpendicular magnetic random memory with high thermal stability. This method is to reorient the magnetization from a perpendicular to an in-plane state, which can be caused by Joule heating the MTJ with thermal barriers above TSR by the injected current pulse. This polarized current can also produce the STT to push the magnetization toward a deterministic perpendicular direction from an in-plane state, when decreasing the magnitude of current pulse. Since the perpendicular anisotropy dominates magnetization switching during cooling, the critical current density is determined by the Joule heating for realization of spin reorientation in this writing method. Macrospin modeling shows the critical current density is 2×106A/cm2, which is two orders magnitude lower than that of conventional STT switching. This writing method can be applied to the perpendicular magnetic tunnel junction comprised of Co/Ni multilayer or composite layer.