We have studied the spin-orbit torques in perpendicularly magnetized Hf/CoFeB/MgO system, by systematically varying the thickness of Hf underlayer. We have observed a sign change of effective fields between Hf thicknesses of 1.75 and 2 nm, indicating that competing mechanisms, such as the Rashba and spin Hall effects, contribute to spin-orbit torques in our system. For larger Hf thicknesses (>2 nm), both the components of spin-orbit torques arise predominantly from the bulk spin Hall effect. We have also confirmed these results using spin-orbit torque induced magnetization switching measurements. Our results could be helpful in designing Hf based SOT devices.
Hf thickness dependence of spin-orbit torques in Hf/CoFeB/MgO heterostructures
Rajagopalan Ramaswamy, Xuepeng Qiu, Tanmay Dutta, Shawn David Pollard, Hyunsoo Yang; Hf thickness dependence of spin-orbit torques in Hf/CoFeB/MgO heterostructures. Appl. Phys. Lett. 16 May 2016; 108 (20): 202406. https://doi.org/10.1063/1.4951674
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