The optical magnetoelectric (ME) effect, i.e., the change of optical absorption upon the reversal of the light propagation direction, has been investigated for a polar ferrimagnet ${\mathrm{G}\mathrm{a}\mathrm{F}\mathrm{e}\mathrm{O}}_3$. For dipole- and spin-forbidden $d-d$ transition bands located at 1.2–2.3 eV, a clear signal of the optical ME effect ($\Delta \alpha t\sim 3\times {10}^{-3}$) is observed with an applied magnetic field as low as 500 Oe and a sample thickness ($t$) of $50\mu \mathrm{m}$. The observation of a large ME effect in the present compound suggests a possible route to magnification of this novel phenomenon for application.

• Received 25 December 2003

DOI:https://doi.org/10.1103/PhysRevLett.93.037403