Multi‐Mechanism Synergy in Graphene‐(Fe ₃ O ₄ / FeO )@Carbon Core–Shell Structure Composites for Enhanced Broadband Microwave Absorption

ABSTRACT This study successfully constructed (Fe ₃ O ₄ /FeO)@carbon core–shell structure composites (F@C) with multiple heterogeneous interfaces via an in situ carbonization‐phase transition coupling strategy, leveraging the structural modulation principles of spinel‐type ferrites. Material characterization results indicate that the (Fe ₃ O ₄ /FeO)@C composite in this system exhibits high saturation magnetization properties. Investigation of electromagnetic loss mechanisms demonstrated that defects and oxygen‐containing functional groups in graphene promote electron‐leap conduction, while the magnetic coupling effect at the Fe ₃ O ₄ /FeO heterointerface significantly enhances electromagnetic energy dissipation. When the F@C content was 20% with 5 wt% GR loading, the composite exhibited exceptional broadband absorption in the Ku band. At a matched thickness of 1.55 mm, the G5 sample achieved a minimum reflection loss of −55.54 dB at 15.12 GHz and an effective absorption bandwidth of 4.8 GHz (13.2–18 GHz). Radar cross‐sectional simulations further confirmed that the G5 sample absorbs 88.89% of incident electromagnetic wave energy within a θ = ±90° incidence range. By synergistically optimizing crystal phase transition engineering and interface polarization modulation, this work establishes a magnetic‐dielectric parameter matching model, providing critical theoretical and technical foundations for developing advanced ultrathin broadband microwave absorbers.