Magnetic‐Dielectric Complementary Fe‐Co‐Ni Alloy/Carbon Composites for High‐Attenuation C‐Band Microwave Absorption via Carbothermal Reduction of Solid‐Solution Precursor

Abstract Ferromagnetic alloys/carbon composites with excellent electrical and magnetic properties are highly desirable as electromagnetic wave absorption materials, but achieving high‐attenuation performance in C‐band (4–8 GHz) remains a challenge. Herein, a direct carbothermal reduction of organic gluconate solid‐solution precursor method is developed to synthesize ferromagnetic Fe‐Co‐Ni alloy/carbon composites, which realize high‐attenuation electromagnetic wave absorption in C‐band. By virtue of Fe, Co, and Ni elements homogeneously dispersing at the molecular level in the solid‐solution precursor with the regulated mole ratio, serial FeCo2Ni/C, Co7Fe3/C, FeNi3/C, and Co3Ni/C composites can be deliberately prepared. First‐principles calculations and off‐axis electron holograms can clearly unravel that these Fe‐Co‐Ni alloys could perform as excellent dielectric‐magnetic complementary loss units to trigger synergistic electronic dipole polarization oscillation, magnetic moment resonance, and magnetic coupling interaction. Meanwhile, the rich alloy–carbon interfaces and conductive carbon skeleton can facilitate delightful interfacial polarization and conductive loss. Combining these positive electromagnetic energy dissipation characteristics, FeCo2Ni/C with strengthened dipole polarization oscillation and outstanding impedance matching realizes an extremely high‐attenuation absorption performance with a minimum reflection loss of −82.2 dB at 5.21 GHz. This work provides a feasible and flexible insight into producing magnetic‐dielectric complementary Fe‐Co‐Ni alloys/carbon composites with various alloy compositions as excellent electromagnetic wave absorbers.