Defect engineering unlocks intrinsic magnetism of α-MnO₂ for wideband microwave absorption

Efficient electromagnetic wave absorption (EWA) is essential for stealth technology and signal integrity, yet the development remains constrained by the trade-off between attenuation capacity and impedance matching. While the incorporation of magnetic phases can enhance impedance matching, it typically increases material density, which is detrimental to lightweight design. Herein, we demonstrate that Ni doping combined with oxygen vacancies (O_v) engineering induces a magnetic response in α-MnO₂ through local lattice distortion and defect-mediated spin asymmetry, thereby introducing frequency-dispersive magnetic-loss pathways. O_v introduces Mn 3d-derived defect states with uncompensated spins, while Ni–Mn 3d hybridization amplifies local symmetry breaking, consistent with enhanced local magnetic correlations. These effects, together with relaxation-dominated polarization loss at defect sites and carbon-coupled interfaces, establish dual-loss mechanisms that synergistically improve impedance matching and broaden the electromagnetic absorption bandwidth (EAB). Consequently, the materials achieve an effective EAB (RL ≤ -10 dB) of 5.24 GHz at a thickness of 1.65 mm and a minimum reflection-loss (RLmin) of -54.98 dB at 2.10 mm, with a low filler loading of 29 wt%. Furthermore, the material significantly reduces far-field scattering without requiring extrinsic magnetic additives. This work highlights defect engineering as a promising strategy to co-regulate magnetic and dielectric responses for next-generation, lightweight broadband EWA.