Magnetoplasmonic Gratings Induced an Unusual Magneto‐Optical Kerr Effect at Optical Frequencies

Abstract Transverse magneto‐optical Kerr effect (TMOKE) has attracted much attention due to its widespread application in nonreciprocal photon and sensing devices. The vast majority of studies related to TMOKE are mainly focused on p‐polarized incidence as a result of the stereotype that only p‐polarized incidence can generate TMOKE in conventional magnetic materials. Thanks to the powerful ability of metamaterials to regulate light, in recent years, the TMOKE under s‐polarized incidence is explored and observed successfully. Nevertheless, different from the universality and high amplitude of p‐polarized TMOKE, the excitation of s‐polarized TMOKE is pretty rare, and the peak values of s‐polarized TMOKE in the reported research are really weak, which limits its application potential to a large extent. Here, the iron‐based grating structure is proposed that excites surface plasmon polaritons (SPPs) and then causes the highest peak value of s‐polarized TMOKE at optical frequencies to date, which is seven orders of magnitude higher than that of the planar Fe film. Besides, its refractive index sensitivity reaches up to 685 nm RIU −1 . The work broadens the design path of s‐polarized TMOKE as a promising candidate to promote the development of novel magnetoplasmonic sensors and nonreciprocal photon devices.