Hierarchical core-shell FeCo@SiO2@NiFe2O4 nanocomposite for efficient microwave absorption

Narrow absorption band width is a common problem faced by current electromagnetic wave absorbing materials. It is urgent but challenging to explore new design solutions to solve this problem. Herein, a core-shell FeCo@SiO2 @NiFe2O4 composite was prepared by chemical co-precipitation method. The effects of calcination temperature on the structure of the cladding layer, magnetic properties and wave absorption properties of the composite powder were investigated. Results showed that the particles of NiFe2O4 @SiO2 cladding layer uniformly covered on the surface of FeCo powder gradually gathered and grew with the increase of calcination temperature from 500 to 800 ℃, resulting in the destruction of the local structure of the coating layer. The composite powder calcined at 700 ℃ has a uniform and dense coating layer structure, and has high saturation magnetization, high coercivity and excellent electromagnetic wave absorption performance. Consequently, the composite powder calcined at 700 °C has a maximum reflection loss of −52.38 dB with a frequency of 9.5 GHz when the matching thickness is 2.65 mm, and the EAB is up to 8.5 GHz with a matching thickness of 2.24 mm. The electromagnetic wave loss mechanism of the powder originates from the excellent impedance matching characteristics, high electromagnetic wave attenuation constant, multiple dielectric relaxation processes, multiple interface polarizations and high magnetic loss as well as high dielectric loss capability.