Constructing FeCoNi@graphene core–shell architectures via Joule flash to achieve efficient electromagnetic wave absorption

The increasingly complex electromagnetic environment demands electromagnetic wave absorption materials that are thin, broadband, and engineering-scalable; however, achieving excellent impedance matching while maintaining high-efficiency electromagnetic attenuation remains a major technical challenge. Here we propose a second-scale, high-temperature in situ synthesis strategy based on Joule flash heating. Under extreme conditions approaching 2000 ℃, this method enables the efficient fabrication of reduced graphene oxide (rGO)-encapsulated binary and ternary Fe–Co–Ni nanoalloys (FeNi@rGO, CoNi@rGO, FeCo@rGO and FeCoNi@rGO). The resulting composites feature a continuous conductive network and intimate magnetic–dielectric interfaces, where the synergy between dielectric loss and magnetic loss markedly improves impedance matching. The composites deliver a minimum reflection loss as low as −56.1 dB at a matching thickness of only 1.5 mm, together with a broadband absorption bandwidth of up to 4.4 GHz. These results highlight the strong potential of this material platform for high-performance electromagnetic wave absorption applications. This work not only offers an efficient and green route to advanced electromagnetic wave absorbers, but also provides new insights into the understanding and regulation of coupled dielectric–magnetic loss mechanisms in composites, thereby enabling the rational design of high-performance absorbers.