Dual-layer coating Co@Fe@Fe3O4 heterogeneous magnetic particles and their electromagnetic absorption properties

By chemical liquid-phase reduction combined with in situ self-oxidation dual-layer core-shell structured heterogeneous Co@Fe@Fe3O4 particles were synthesized. The effects of oxidation conditions on the microstructure, static magnetic properties, and electromagnetic wave absorption performance of heterogeneous Co@Fe@Fe3O4 particles were investigated. The findings indicate that the heterogeneous Co@Fe@Fe3O4 particles are primarily composed of three elements: Co, Fe, and O, displaying a typical core-shell structural characteristic, with shell layer thicknesses of approximately 170 nm for Fe and 140 nm for Fe3O4. The specific saturation magnetization and remanent magnetization have not change significantly with the increase of oxidation temperature but coercivity changes notablely with the increase of oxidation temperature and presenting increasing trend, reached maximum value at 70 °C oxidation temperature. In situ self-oxidation process significantly enhances the dielectric loss tangent of the heterogeneous Co@Fe@Fe3O4 particle samples, while the magnetic loss tangent shows a decline. Typical polarization loss and electrical conductivity loss can be observed for the particles and magnetic loss is primarily dominated by natural resonance. At an oxidation temperature of 60 °C, the heterostructured Co@Fe@Fe3O4 particle samples exhibited the highest attenuation constant α and optimal wave absorption performance, achieving minimum reflection loss of −20.25 dB and maximum effective absorption bandwidth of 4.48 GHz.