Broadband and Wide‐Angle Nonreciprocal Electromagnetic Transport via Gradient Permeability‐Near‐Zero Metastructures

ABSTRACT Breaking time‐reversal symmetry to achieve broadband and wide‐angle nonreciprocity is critical in electromagnetic waves manipulation. While Epsilon‐Near‐Zero materials have revolutionized the control of Transverse Magnetic modes, realizing comparable broadband nonreciprocity for Transverse Electric (TE) modes remains a formidable challenge because the permeability of the magneto‐optical materials is isotropic. Here, we propose a novel strategy utilizing gradient Permeability‐Near‐Zero (PNZ) subwavelength magnetic metastructures based on yttrium iron garnet thin films. By engineering the magnetic permeability tensor near the zero‐index regime, we excite robust TE‐polarized leaky modes (analogous to magnetic Berreman modes) in deep sub‐wavelength films (< λ /100, λ is wavelength). This mechanism unlocks a continuous nonreciprocal window, achieving a maximum nonreciprocity of 0.93 (approx. 12.4 dB) across the entire 35–40 GHz band. Unlike resonance‐dependent metastructures, our design exhibits intrinsic robustness, maintaining high performance over an exceptionally wide incidence angle range (> 40°) and thickness tolerances (−28% to +24%). This work fills the critical gap in magnetic light–matter interactions, offering a scalable and robust material platform for next‐generation directional electromagnetic energy transport, emission control, and signal isolation.