Observation of antiferromagnetic domains in Cr2O3 using nonreciprocal optical effects

Abstract

The archetypal magnetoelectric (ME) antiferromagnet ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$, which has the diagonal components of linear ME tensor, exhibits several different types of nonreciprocal optical effects: the electric field-induced $(E\text{\ensuremath{-}}\mathrm{induced})$ Faraday effect, the electric field-induced magnetic circular dichroism ($E\text{\ensuremath{-}}\mathrm{induced}$ MCD), and the spontaneous nonreciprocal rotation of reflected light (NRR). In principle, antiferromagnetic (AFM) domains of ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$ are expected to be distinguished by using these effects. However, such domain observations have never been reported mainly due to the smallness of the effects studied to date. In this study, we demonstrate that all these nonreciprocal optical effects allow the observation of AFM domains in ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$. We first measured spectra of the $E\text{\ensuremath{-}}\mathrm{induced}$ Faraday effect and $E\text{\ensuremath{-}}\mathrm{induced}$ MCD, and found that relatively large effects appear in the visible light region. Then, by imaging spatial distributions of the three nonreciprocal effects via field and light-polarization modulation imaging techniques, we succeeded in visualizing AFM domains. Intriguingly, the domain patterns obtained via the bulk sensitive $E\text{\ensuremath{-}}\mathrm{induced}$ Faraday effect and MCD and those via the surface-sensitive NRR are identical to each other, revealing that the AFM domains in ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$ are uniform in the thickness direction. The domain observation methods provided here will be widely applied to various ME antiferromagnets, not only insulators but also metals, with the diagonal components of linear ME tensor.