The electromagnetic loss enhancement mechanism of helical carbon-based composites under spin state regulation.

Carbon-based microwave absorbing materials are limited by unbalanced electromagnetic responses and narrow-band absorption due to single conductive or polarization loss mechanisms. To address this bottleneck, we developed a low-cost combustion-induced self-propagating coupled annealing strategy to fabricate structurally controllable iron-tin sulfide nanoparticles uniformly decorated on chiral carbon nanocoil (CNC) supports. The transient self-propagating high-temperature effect drives rapid phase transformation and lattice reconstruction, while the intrinsic chiral asymmetry of CNCs induces lattice symmetry breaking and abundant defects, enabling precise regulation of electron spin-orbit coupling. Combined with microstructural characterization, electromagnetic measurements, and finite-element simulations, we demonstrate that lattice distortion and sulfide-induced defects effectively lift electron spin channel degeneracy, activate multidimensional spin responses, and significantly enhance the electronic density of states near the Fermi level. The constructed gradient heterostructures and multiscale polarization centers optimize impedance matching while synergistically boosting dielectric polarization loss and spin-mediated magnetic loss. The optimized CNC@FeSnSM sample achieves an ultrawide effective absorption bandwidth of 6.08 GHz at 3.1 mm thickness and a filling rate of 15% which was 196% higher than that of the control sample. It also exhibited a high reflection loss of -58.93 dB at 11 GHz, demonstrating both a wide bandwidth and strong absorption characteristics. This work provides a new paradigm for high-performance carbon-based sulfide microwave absorbers through the coupling of chiral structures and spin control engineering.