Faraday effect in $\mathrm{FeBO}_3$ caused by the magnetization component parallel to the $\mathrm{C}_3$ axis

The Faraday effect in the rhombohedral weak ferromagnet $\mathrm{FeBO}_3$, which is due to the magnetization component parallel to the $\mathrm{C}_3$ axis of the crystal, is predicted and experimentally observed for the first time. This magnetization component is almost three and a half orders of magnitude smaller than the magnetization in the basal plane. The measured effect is six orders of magnitude smaller than the Faraday effect caused by the magnetization in the basal plane. The origin of the significant difference in the magnitudes of the Faraday effect due to the magnetization in the basal plane and to the magnetization parallel to the $\mathrm{C}_3$ axis is discussed.