Modulation of thermal stability and spin-orbit torque in IrMn/CoFeB/MgO structures through atom thick W insertion

Antiferromagnet (AFM)/ferromagnet (FM) systems such as IrMn/CoFeB/MgO enable spin-orbit-torque- (SOT-) induced switching of perpendicular magnetization in the absence of an external magnetic field. However, the low thermal stability, weak perpendicular magnetic anisotropy (PMA), and indistinctive SOT of these AFM/FM heterostructures pose challenges to the practical application. Here, through the insertion of a thin W layer between the IrMn and CoFeB layers, we show that much larger effective PMA fields are obtained with annealing stability to 300 degrees C, which is guaranteed by the prevention of Mn diffusion via W insertion as shown in spherical aberration corrected transmission electron microscopy and atomic-resolution electron energy-loss spectroscopy measurement results. Furthermore, the spin-orbit torque is effectively tuned by changing the W layer thickness via modulation of the interfacial spin-orbit coupling at IrMn/W/CoFeB interfaces, which was reported to degrade the interface spin transparency for the spin currents. Finally, field-free magnetization switching was achieved with comparable exchange bias fields to samples without W insertion. This work demonstrates an effective strategy for improving the performance of the thermally robust AFM-based SOT device.