Measurement of Current Induce Spin Orbit Torque effects using Optical Ferromagnetic Resonance

Pure spin current is a flow of spin angular momentum with no net charge current associated with it and is a key ingredient in Spintronics [1]. In the spin Hall effect (SHE) a charge current is converted into a pure spin current. Measurement of spin currents in a material is usually indirect and challenging. Here we discuss a novel optical technique called the optically detected ferromagnetic resonance (O-FMR) to measure the spin Hall angle (SHA) in a conventional Py|Pt bilayer system [2]. We employ the damping modulation method in our optical technique to determine the SHA. We compare our results to the ones obtained by the analogous electrical technique called spin torque ferromagnetic resonance (ST-FMR) on the same sample and show that the damping in the O-FMR can be extracted at higher current densities. Thus, the SHA can be more accurately determined indicating a substantially higher noise floor of the STFMR method. Our work leads to better understanding of the limitations of SHE measurements.

[1] S. S. P. Parkin et. al, “Magnetic domain-wall racetrack memory,” Science. 2008.
[2] A. Capua, et. al., “Phase-resolved detection of the spin Hall angle by optical ferromagnetic resonance in perpendicularly magnetized thin films,” Phys. Rev. B, vol. 95, no. 6, pp. 2–7, 2017.