Comparative Study of Current-Induced Torque in Cr/CoFeB/MgO\nand W/CoFeB/MgO

Orbital\ntorque (OT) in magnetic heterostructures has been actively\ndiscussed in terms of its actual existence and usefulness in comparison\nto the spin-orbit torque (SOT) that shows promise for next-generation\nmagnetoresistive random access memories. The objectives of this study\nare 2-fold: (i) making an apples-to-apples comparison in two representative\nstacks where OT and SOT are expected to dominate and (ii) examining\nthe potential emergence of OT in archetypal SOT stacks. Cr/CoFeB/MgO\nand W/CoFeB/MgO are chosen as the OT- and SOT-dominant systems, respectively.\nSystematic variations in each layer’s thicknesses reveal that\n(i) Cr/CoFeB/MgO exhibits substantial torque comparable to or even\nexceeding that of the W/CoFeB/MgO stack when Cr and CoFeB layers are\nespecially thick and (ii) the torque in W/CoFeB/MgO changes sign with\nincreasing W and CoFeB thicknesses, suggesting a crossover of the\ndominant mechanism from SOT to OT. The findings clarify the opportunities\nand challenges of devices leveraging SOT and OT.