Multifunctional Magneto‐Optical Metagrating With Strong Optical Gyromagnetic Effect and High Faraday Rotation

Magneto‐optical (MO) materials serve as a cornerstone in the field of nonreciprocal devices owing to time‐reversal breaking. While at optical frequencies, the gyromagnetic effect cannot be observed in conventional magnetic materials due to the mismatch between low‐frequency Larmor precession and high‐frequency incident light. Recent developments of MO metamaterials with artificial gyromagnetic properties bring a significant breakthrough in design freedom for the manipulation of light waves. The long‐sought optical gyromagnetic activity can induce a transverse magneto‐optical Kerr effect (TMOKE) under s‐polarized light, which is a novel MO phenomenon unachievable in natural materials. However, the currently reported values of permeability (µ) off‐diagonal elements and s‐polarized TMOKE are pretty small, severely inhibiting the practical applications of MO devices. Here we propose a meta‐grating nanostructure that excites surface plasmon resonance and waveguide modes, causing a significant enhancement of the local magnetic field in the MO medium. It exhibits the highest experimental value of s‐polarized TMOKE (∼0.184) and the record‐high effective off‐diagonal element of µ (∼0.46), which is more than four orders of magnitude higher than that of the planar MO film. Furthermore, the meta‐grating simultaneously possesses strong p‐polarized TMOKE and high Faraday rotation (FR), demonstrating its great potential for multifunctional nonreciprocal devices.