Large Field-like Spin-Orbit Torque and Enhanced Magnetization Switching Efficiency Utilizing Amorphous Mo.

Spin-orbit torque magnetic random access memory (SOT-MRAM) has great promise in high write speed and low power consumption. Mo can play a vital role in constructing a CoFeB/MgO-based MRAM cell because of its ability to enhance the perpendicular magnetic anisotropy (PMA), thermal tolerance, and tunneling magnetoresistance. However, Mo is often considered as a less favorable candidate among SOT materials because of its weak spin-orbit coupling. In this study, we experimentally investigate the SOT efficiencies in Mo/CoFeB/MgO heterostructures over a wide range of Mo thicknesses and temperature. Decent damping-like SOT efficiency |ξDL| = 0.015 ± 0.001 and field-like SOT efficiency |ξFL| = 0.050 ± 0.001 are found in amorphous Mo. The ξFL/ξDL ratio is greater than 3. Furthermore, efficient current-induced magnetization switching is demonstrated with the critical current density comparable with heavy metal Ir and W. Our work reveals new understanding and possibilities for Mo as both an SOT source component and PMA buffer layer in the implementation of SOT-MRAMs.