Intrinsic Solution to the Dilemma between High-Efficiency and External-Field-Free Spin-Orbit Torque Switching Based on Biaxial Devices.

Spin-orbit torque (SOT) is widely considered to be a fast and robust writing scheme for magnetic random-access memories (MRAMs). However, the requirements of field-free switching and high switching efficiency are often incompatible in SOT devices, placing a critical challenge on its improvement. Here we propose that by utilizing biaxial systems the dilemma between high-efficiency and external-field-free SOT switching can be solved intrinsically. We further demonstrate the feasibility of the proposed writing scheme in a MgO/Fe/W device and show that the intrinsic multistate storage ability of the biaxial device compensates its additional area requirement. These results are expected to pave the way toward the further development of SOT-MRAMs.