Critical switching current of a perpendicular magnetic tunnel junction owing to the interplay of spin-transfer torque and spin-orbit torque

Abstract

Using the linearized Landau–Lifshitz-Gilbert (LLG) equation in the rotation coordinate, we calculate the critical switching current density of a perpendicular magnetic tunnel junction (MTJ), where magnetization switching is achieved by the interplay of spin-transfer and spin-orbit torques. In terms of the critical current density, we find that as the current density inducing the spin-orbit torque (jSOT) increases, the current density inducing the spin-transfer torque (jSTT) decreases nonlinearly. In the presence of the spin-orbit field-like torque (β), the critical switching current density by the spin-transfer torque is proportional to the damping constant (α) as the conventional spin-transfer torque switching, while the critical switching current density by the spin-orbit torque increases with α when Heff≫HSOT . We also investigated the β dependence of the critical switching current density. For a given jSOT , the critical switching current density for the spin-transfer torque, jSTT,c decreases linearly with increasing β and nonlinearly decreases with increasing jSOT for a given β. Further, we discuss the β dependence of the critical switching current density on energy.