Electromagnetic wave absorbing properties of multi-layer heterogeneous Co@Co_xFe_1-x@Fe@Fe₃O₄@C particles

Based on chemical liquid-phase reduction composite high-temperature carbonation technique, different carbon-coated four-layer core-shell heterogeneous Co@Co_xFe_1-x@Fe@Fe₃O₄@C particles were synthesized. The variation of the thickness of the carbon coating layer and the morphological characteristics, magnetic properties, and electromagnetic wave absorption performance of heterogeneous Co@Co_xFe_1-x@Fe@Fe₃O₄@C particles were investigated. The study shows that the heterogeneous Co@Co_xFe_1-x@Fe@Fe₃O₄@C particles are primarily composed of Co, Fe, C, and O elements, inheriting good structural characteristics from heterogeneous Co@Fe@Fe₃O₄ particles. When the oleic acid amounts are 0.1 ml, 0.5 ml, and 1 ml, the thickness of the carbon coating layer is 2–3 nm, 4–5 nm, and 5–6 nm, respectively. At an oleic acid amount of 0.5 ml, the degree of graphitization of the carbon coating layer is the highest. For heterogeneous Co@Co_xFe_1-x@Fe@Fe₃O₄@C particles with carbon coating layer thickness of 2–3 nm at sample thickness of 1.5 mm the minimum reflection loss was −44.84 dB with a maximum effective absorption bandwidth of 4.88 GHz. When the carbon coating layer thickness was 4–5 nm, the heterogeneous Co@Co_xFe_1-x@Fe@Fe₃O₄@C particles exhibited optimal absorption performance with a minimum reflection loss of −48.54 dB with 2.3 mm thickness and maximum effective absorption bandwidth of the sample was 5.44 GHz. The absorption mechanism of the composite material was presented and which includes the irregular shape of the heterogeneous Co@Co_xFe_1-x@Fe@Fe₃O₄@C which facilitates multiple scattering and reflection of electromagnetic waves within and between particles increasing the attenuation and dissipation of electromagnetic waves; the heterogeneous Co@Co_xFe_1-x@Fe@Fe₃O₄ particles maintain good magnetic loss capabilities during the composite process with carbon; the introduction of amorphous carbon increases the heterogeneous interfaces between the carbon shell and the magnetic metal materials, inducing interfacial polarization, providing aggregation centers for charges and dipoles and optimizing impedance matching performance allowing more electromagnetic waves to enter the absorption material and enhancing the attenuation capability of electromagnetic waves.