Manganese ferrite-modified coal gangue for C-band microwave absorption based on magnetic-dielectric synergistic optimization

This study aims to develop a high-performance, low-cost low-frequency electromagnetic (EM) wave absorbing material to address the growing issue of low-frequency EM pollution caused by devices such as 5G/6G, radar, and WiFi. By combining hydrothermal synthesis and high-temperature carbonization, a ternary composite material, MnFe2O4/C/CG (MFC), was successfully prepared with coal gangue (CG) as the matrix. The CG and the surface-deposited carbon layer possess abundant oxygen-containing functional groups and defect structures, which not only provide heterogeneous interfaces and enhance dielectric loss but also improve the dispersion of MnFe2O4 particles. Meanwhile, the MnFe2O4 particles contribute crucial magnetic loss capability, achieving a magneto-dielectric synergy. The results show that the MFC-2 sample exhibits strong​ low-frequency wave-absorbing performance in the C-band, achieving a minimum reflection loss of −57.82 dB and an effective absorption bandwidth of 3.54 GHz at a thickness of 4.86 mm, which covers the N79 band and 88.5% of the C-band. Its excellent performance is attributed to favorable impedance matching and a magneto-dielectric synergistic loss mechanism involving interfacial polarization, dipole polarization, and magnetic loss. This work provides a feasible strategy for developing high-performance, low-cost low-frequency wave-absorbing materials using bulk solid waste CG.