Sagnac interferometry for high-sensitivity optical measurements of spin-orbit torque

TL;DR

This paper demonstrates that Sagnac interferometry significantly enhances the sensitivity of optical measurements of spin-orbit torque, enabling more accurate and artifact-free quantification in thin magnetic films with various anisotropies.

Contribution

The study introduces the application of Sagnac interferometry for high-sensitivity, quantitative optical measurement of spin-orbit torque in thin magnetic samples, surpassing conventional Kerr effect methods.

Findings

Sagnac interferometry improves signal-to-noise ratio for magnetic measurements.

It allows quantitative analysis of spin-orbit torque in thin films with perpendicular anisotropy.

It provides a cross-check for electrical measurement techniques, identifying potential artifacts.

Abstract

Sagnac interferometry can provide a significant improvement in signal-to-noise ratio compared to conventional magnetic imaging based on the magneto-optical Kerr effect (MOKE). We show that this improvement is sufficient to allow quantitative measurements of current-induced magnetic deflections due to spin-orbit torque even in thin-film magnetic samples with perpendicular magnetic anisotropy for which the Kerr rotation is second-order in the magnetic deflection. Sagnac interfermometry can also be applied beneficially for samples with in-plane anisotropy, for which the Kerr rotation is first order in the deflection angle. Optical measurements based on Sagnac interferometry can therefore provide a cross-check on electrical techniques for measuring spin-orbit torque. Different electrical techniques commonly give quantitatively inconsistent results, so that Sagnac interferometry can help to identify which techniques are affected by unidentified artifacts.