Defect-interface engineering optimizes polymetallic sulfides-based absorbers toward high-efficiency low-/middle-frequency electromagnetic wave absorption

Overcoming the challenge of decoupling impedance matching from attenuation for low-frequency (2–10 GHz) electromagnetic wave absorption, this work presents a defect-engineered multiphase medium-entropy sulfide composite. Synthesized via integrated mechanical alloying and surfactant-assisted hydrothermal sulfidation, the composite integrates sulfur vacancy-rich (Fe,Co,Ni)9S8, anisotropic FeCoNi alloy, CoFe₂O₄, and porous MoS2. This architecture creates abundant heterogeneous interfaces and interfacial sulfur vacancies, significantly enhancing defect-induced polarization and dielectric loss via the “Janus effect.” Concurrently, the magnetic components boost magnetic loss while optimizing impedance matching. Benefiting from this magneto-dielectric synergy, the composite achieves exceptional absorption: a minimum reflection loss (RLmin) of -50.4 dB at 3.96 GHz and a remarkable RLmin -77.5 dB at 9 GHz. Radar cross-section simulations confirm application potential. This work provides strategic insights for designing innovative low-/mid-frequency absorbers through synergistic dielectric-magnetic loss in polymetallic sulfide heterostructures.