Breaking the low-frequency electromagnetic absorption barrier via FeCoNi medium-entropy alloy-enabled carbon reconstruction and dielectric-magnetic coupling

Efficient low-frequency electromagnetic wave absorption remains intrinsically challenging due to the conflicting requirements of impedance matching and energy dissipation under long-wavelength conditions. In lightweight carbon-based systems, the lack of coordinated dielectric–magnetic response further limits attenuation at low frequencies. Here, a medium-entropy FeCoNi alloy is introduced as a multifunctional regulator to simultaneously engineer carbon structure and electromagnetic response. The alloy catalyzes low-temperature graphitization to construct conductive networks, while its intrinsic magnetic properties enable dielectric–magnetic coupling. This integrated regulation establishes a synergistic dissipation mechanism that optimizes impedance matching and shifts attenuation toward lower frequencies. The confined FeCoNi@N-doped carbons exhibit a minimum reflection loss of −62 dB at 6.1 GHz, with an effective absorption bandwidth of 3.6 GHz, covering 90% of the C band. By further tailoring dielectric dispersion, the absorption extends toward the S band, achieving −52 dB at 4.8 GHz and 99% absorption from 3.6 GHz to 4.0 GHz. Moreover, integration into porous composite fibers via microphase separation introduces additional interfacial polarization and multiple scattering, enabling −55 dB attenuation and regulated X-band response. This work provides a viable strategy for achieving low-frequency absorption in lightweight materials through coordinated regulation of carbon architecture and dielectric–magnetic coupling. Download: Download high-res image (424KB) Download: Download full-size image