Artifact-free method of measuring spin-orbit torque

Modern magnetic memory devices depend on the ability to control magnetization via spin-orbit torque to enable the read and write functions. In order to further improve the efficiency of such devices, the underlying mechanism of spin-orbit torque needs to be better understood.

Electrical methods of quantifying spin-orbit torque have suffered from artifacts arising from planar-Hall and anomalous-Nernst effects. A new article by Kim et al. reports a method that circumvents such artifacts by utilizing optical measurements. Instead of the traditional electrical method, in which both the manipulation and the detection of the magnetization state are accomplished by an electric current, the new method, while still using an electric current to manipulate the magnetization, utilizes a magneto-optical effect to detect it. This allows the polarization state of the light to be changed without affecting the magnetization state.

Using Jones-matrix calculus, the researchers designed a setup free from the optical version of similar artifacts, such as the planar Hall effect. In addition, the setup was created with photoelastic modulation and balanced detection, which makes it accessible to conventional setups.

The researchers tested their setup with a metallic stack of Pt/Py bilayers. Their experimental results confirmed that it was free from the optical planar Hall effect and anomalous-Nernst effects. Their setup should permit a more efficient way to study artifact-free spin-orbit torque effects. It is similar to conventional photoelastic modulation setups, and thus can readily be integrated in future experimental studies.

Source: “Artifact-free optical spin-orbit torque magnetometry,” by Joo-Sung Kim, Yong-Keun Park, Hyun-Seok Whang, Jung-Hyun Park, Byoung-Chul Min, and Sug-Bong Choe, Applied Physics Letters (2019). The article can be accessed at https://doi.org/10.1063/1.5087743 .