Near-normal nonreciprocal thermal radiation with a 0.3T magnetic field based on double-layer grating structure

The violation of Kirchhoff's law is anticipated to manipulate the emissivity and absorptivity separately and offer new freedom and opportunity for high-efficiency energy harvesting. However, the current designs of nonreciprocal thermal emitters encounter challenges related to large magnetic fields and large incident angles, hindering the practical implementations and applications. This study introduces a novel design involving a metal-SiC grating positioned above a magneto-optical (MO) film, allowing for the generation of robust nonreciprocal thermal radiation in close proximity to the normal direction with a moderate magnetic field of 0.3T. Such magnetic field strength is within the reach of a permanent magnet, which is conducive to practical applications. The manifestation of this phenomenon can be primarily attributed to the guided mode resonance occurring in the low-loss SiC grating, which can enhance the sensitivity to the magnetic field. In addition, the influences of the incident angle and structural dimension parameters on nonreciprocity are also investigated. It is found that this structure can not only realize nonreciprocity at ultra-small angles, but also realize directional nonreciprocal thermal radiation, which greatly expands the applicability of the structure. The present findings remove the limitations of large magnetic field and incident angle for traditional nonreciprocal thermal radiation, and promote the practical realization and application of nonreciprocal thermal emitters.