Cubic magneto-optic Kerr effect in $\mathrm{Ni}$(111) thin films with and without twinning

In most studies utilizing the magneto-optic Kerr effect (MOKE), the detected change of polarized light upon reflection from a magnetized sample is supposed to be proportional to the magnetization $M$. However, MOKE signatures quadratic in $M$ have also been identified and utilized, e.g., to sense the structural order in Heusler compounds, to detect spin-orbit torque or to image antiferromagnetic domains. In our study, we observe a strong anisotropic MOKE contribution of third order in $M$ in $\mathrm{Ni}$(111) thin films, attributed to a cubic magneto-optic tensor $\propto M^3$. We further show that the angular dependence of cubic MOKE (CMOKE) is affected by the amount of structural domain twinning in the sample. Our detailed study on CMOKE will open up opportunities for CMOKE applications with sensitivity to twinning properties of thin films, e.g., CMOKE spectroscopy and microscopy or time-resolved CMOKE. Furthermore, the in-plane magnetization orientation can be detected with CMOKE when perpendicular incidence light is used, which is suitable for MOKE setups that do not provide oblique incidence.