Constructing porous CoFe₂O₄-Co₃Fe₇@C nanoflakes with tunable Co₃Fe₇ ratio for wideband microwave absorption at thin matching thickness

The flake-like magnetic materials with intrinsic anisotropy show promise for electromagnetic absorption, however, their absorption performance remains challenged by impedance mismatch and high matching thickness caused by a lack of reasonable composition and structure design. This work synthesized the novel porous CoFe₂O₄-Co₃Fe₇@C nanoflakes (NFs) by the hydrothermal method and hydrogen reduction. The CoFe₂O₄@C composite with a carbon-coated core-shell structure was synthesized via a dopamine-mediated approach and high-temperature calcination, followed by precisely controlled hydrogen reduction at varying temperatures to fabricate porous CoFe₂O₄-Co₃Fe₇@C NFs with tunable Co₃Fe₇ phase content. Notably, samples reduced at 300 °C achieved minimum reflection loss (RL_min) values of −119.7 dB, with thin matching thicknesses of 1.8 mm. Meanwhile, it exhibited maximum effective absorption bandwidths (EAB) of 9.2 GHz, significantly superior to most CoFe-based absorbers. The distinctive flake-like morphology and porous structures, coupled with abundant heterogeneous interfaces brought by the presence of CoFe₂O₄ and Co₃Fe₇ phase facilitate multiple polarization mechanisms, enhancing dielectric loss, which, together with well-matched magnetic losses enhanced by the Co₃Fe₇ phase, significantly augments the absorption performance. This study highlights the potential of CoFe₂O₄-Co₃Fe₇@C NFs as promising candidates for high-efficiency microwave absorbers and proposes novel design strategies for developing broadband microwave absorbers with thin matching thickness.