Characterization of Spin-Orbit Torque Efficiency in the RF Regime for MRAM Applications

Magnetization in a magnetic heterostructure is known to process with radio frequency (rf) excitations. Such high frequency magnetic dynamics are often employed to characterize key parameters for magnetic random access memory (MRAM) applications. One of the most popular approaches, spin torque ferromagnetic resonance (ST-FMR), has been developed to explore the intrinsic magnetic and spin transport properties in various types of magnetic heterostructures by applying rf excitations onto micron-sized devices, from which the charge-to-spin conversion efficiency or the so-called spin-orbit torque (SOT) efficiency can be quantified. In this work, we systematically study and compare the estimated SOT efficiencies of W-based magnetic heterostructures through three different variations of the STFMR technique: (1) thickness-dependent torque ratio analysis, (2) dc-modulation of ST-FMR, and (3) direct current-induced SOT switching. Our results reveal that the estimated SOT efficiencies obtained from the above approaches show significant discrepancies. The thickness-dependent torque ratio analysis is able to evaluate the intrinsic SOT parameters more accurately. Possible overestimations may be introduced in the other two approaches.