Determination of the spin Hall angle by the inverse spin Hall effect and the spin torque ferromagnetic resonance: comparison of methods

Abstract

The spin torque ferromagnetic resonance (STFMR) is one of the popular methods for measurement of the spin Hall angle (SHA) and is very easy to implement. However, in order to accurately determine the SHA, the acquired data must be carefully analyzed: extraction of the SHA requires that the resonance linewidth be determined with an accuracy of a fraction of the Oe which is achieved by solving a multi-parameter optimization problem, typically six parameters. Additionally, the STFMR signal often deteriorates when DC current is passed through the device. In this work we measure the SHA from DC bias current dependent inverse spin Hall effect (ISHE) measurements which is more immune to the injected DC current noise and to the artefacts related the optimization problem. A comparison to the STFMR method is made. The study is complemented by a third direct measurement of the FMR response in the presence of charge current on the same device which is probed using a heterodyne detection scheme. Possible artefacts of the methods are discussed and ways to overcome them for better determination of the SHA. The conclusions of our work lead to a more accurate determination of the SHA and will assist in the search for novel materials for energy efficient spin-based applications.