Reconfigurable Giant Nonreciprocity at Near‐Normal Incidence via Phase‐Change Magneto‐Optical Metagratings

ABSTRACT Breaking Lorentz reciprocity in thermal radiation typically requires extreme grazing angles, suffering from severe geometric projection losses and state volatility. Here, we propose a dynamic, non‐volatile, nonreciprocal absorber integrating a phase‐change (GST) grating atop a magneto‐optical InAs waveguide. Leveraging the transverse magneto‐optical response in the Voigt configuration and precise momentum matching, the metagrating achieves strong nonreciprocal absorption contrast () at a near‐normal incidence angle of under a moderate magnetic field. The device enables continuous spectral steering via incident angle and magnetic field, alongside non‐volatile digital latching of the nonreciprocal state via GST switching. Through non‐Hermitian perturbation theory, we unveil that nonreciprocity quenching during the phase transition originates synergistically from spatial field redistribution and loss‐induced damping. Our findings provide a robust, non‐volatile platform for advanced thermal emission control.