Altermagnets have attracted tremendous interest for revealing intriguing physics and promising spintronics applications. In contrast to conventional antiferromagnets, altermagnets break both PT and Tτ symmetries, and simultaneously exhibit spin-split band structures with a vanishing net magnetization. To quantify altermagnetic insulators without conduction electron, we propose to use magneto-optical Kerr effect (MOKE). In particular, we demonstrate not only the giant MOKE responses, but also their connection with the orientations of Néel vectors at room temperature in altermagnetic insulator of composition hematite (α-Fe2O3). Specifically, under the Néel vector along the [1100] axis, we find a giant polar Kerr rotation angle 103.7 mdeg in the (1120) plane, which is allowed by the magnetic space group C2′/c′. Under the Néel vector along the [1120] axis, we find a longitudinal Kerr angle 9.6 mdeg in the (0001 …
https://iopscience.iop.org/article/10.1088/0256-307X/43/2/020713/meta