Magnetoelectric composites can achieve magneto-electric synergy to optimize impedance matching. However, it is challenging to enhance the broadband absorption performance for thin thickness absorbers. Herein, FeNi₃@C composite with magnetic alloy core and N-doped macroporous multilevel layered carbon shell was constructed by hierarchical interface engineering. The uniform multilevel layered carbon shell could induce interfacial polarization and multiple scattering, and further endows enhanced electromagnetic attenuation and optimized impedance matching. An ultra-thin broadband absorber with an effective absorption bandwidth of 7.4 GHz is achieved at a thickness of only 1.6 mm. Moreover, full-band absorption from 2 to 18 GHz at a thickness of 9.8 mm is realized through metastructure design. This work provides an alternative strategy to prepare core–shell structured magnetoelectric composites for ultra-thin and broadband absorbers.

Designing highly reliable and practical microwave absorbers is one of the most important research directions in the microwave absorbing field. Many absorbents suffer from concentration-sensitivity and environmental-sensitivity dilemmas in practical applications. Here, sea urchin-like aggregates of MnO₂ nanotubes were synthesized by a simple hydrothermal method, which exhibit an outstanding impedance matching characteristic. The composites based on sea urchin-like aggregates of MnO₂ nanotubes show excellent microwave absorption performance in a wide concentration domain from 20 wt.% to 70 wt.%, corresponding to electrical conductivities from 1.86 × 10⁻⁷ to 1.85 × 10⁻⁵ S/m. Such a wide concentration range of absorbent for excellent microwave absorption is mainly attributed to the beneficial impedance matching properties of sea urchin-like aggregates of hollow nanotubes. A competitive absorption bandwidth of 3.36 GHz is achieved at 1 mm thickness, which can be broadened to 13.4 GHz by structural design. This work shows a new scheme for designing reliable and practical microwave absorbers benefit from the wide absorbent concentration domain.