Synergic Magnetic–Dielectric Ni/Co‐Anchored Carbon Aerogels From Cellulose Nanofiber Scaffolds for Electromagnetic Shielding, Infrared Stealth, and Secure RFID Technologies

The growing demand for lightweight and sustainable materials capable of managing electromagnetic radiation, thermal signatures, and wireless privacy requires multifunctional architectures. Here, ultralight magnetic‐dielectric carbon aerogels are fabricated from TEMPO‐oxidized cellulose nanofiber (TO‐CNF) networks coordinated with Ni 2+ or Co 2+ ions. During carbonization, the ions are transformed into uniformly distributed ferromagnetic nanodomains embedded within a partially graphitized carbon framework, generating synergistic dielectric and magnetic loss mechanisms. The resulting aerogels exhibit absorption‐dominated electromagnetic interference (EMI) shielding, with Co‐anchored aerogel achieving a total shielding effectiveness of 43.4 dB in the K band at 1.4 mm thickness. The enhanced shielding performance arises from conduction loss, interfacial and dipolar polarization, magnetic loss, and multiple scattering within the porous structure. The aerogels also provide infrared stealth over a substrate‐temperature range of 50–90°C, with the surface remaining markedly cooler than the heated substrate. When integrated with an RFID tag in a vertical‐insertion and angle‐controlled configuration, the aerogel functions as a lossy angular‐gating layer that creates an angle‐dependent readability window, allowing authorized interrogation while suppressing off‐axis tag detection for passive anti‐skimming. Overall, this work offers new opportunities for sustainable materials in wearable electronics, smart logistics, secure identification systems, and defense‐related applications.