Magnetization dynamics induced by the Rashba effect in ferromagnetic films

Manipulating the magnetization of ferromagnets by the current-induced spin-orbit torque has great potential application in the design of low energy consumption spintronic devices. Normally, an external magnetic field is needed for the reversal of current assisted magnetization by the spin-orbit torque. Recently, the switching of magnetization driven by the spin-orbit torque in the absence of an external magnetic field was reported in a Ta/Co20Fe60B20/TaOx system with lateral structural asymmetry. To understand the physics behind this experiment, we performed first principles calculations on the potential profile at the interface between the ferromagnetic film and the wedge-shaped deposited metal oxide in the Ta/Co/TaO system. This revealed that the lateral structural asymmetry generates two additional Rashba interactions which can reduce the minimum external field required to reverse the magnetization. In addition, we derived the Landau-Lifshitz-Gilbert equation from a quantum transport perspective and numerically investigated the magnetization dynamics in ferromagnetic films induced by Rashba interactions including those generated by lateral asymmetry. Our theoretical simulation provides microscopic explanations of experimental observations of magnetization switching in the absence of an external field of devices with lateral structural asymmetry.