A novel composite of FeCO₃ nanoparticles, which are wrapped with reduced graphene oxide (RGO), is fabricated using a facile one-spot solvothermal method. The composite consists of a substrate of RGO and FeCO₃ nanoparticles that are embedded in the RGO layers. The experimental results for the FeCO₃/RGO composite reveal a minimum refection loss (−44.5 dB) at 11.9 GHz when the thickness reaches 2.4 mm. The effective bandwidth is 7.9 GHz between 10.1 and 18 GHz when the refection loss was below −10 dB. Compared to GO and RGO, this type of composite shows better microwave absorption thanks to improved impedance matching. Overall, this thin and lightweight FeCO₃/RGO composite is a promising candidate for absorbers that require both strong and broad absorption.

Cobalt ferrite is synthesized via a simple solvothermal method. Then, the effect of the degree of cobalt-ferrite growth on its morphology, structure, electromagnetic performance, and microwave absorption is studied as a function of the solvothermal reaction time. When the reaction time during synthesis is 8 h, the structure of cobalt ferrite is hollow spheres. In addition, when the reaction time is 12 h and 16 h, it becomes a submicron sphere with a diameter of 100–150 nm. With the increase of reaction time, cobalt ferrite underwent the process of cobalt ferrite formation, hollow structure formation, hollow structure disappearance, agglomeration separation and reagglomeration in 4–16 h. In general, CoFe₂O₄-8h shows better microwave absorption-the effective absorption bandwidth is 9.84 GHz (6–15.84 GHz) for a thickness of 1.72–3.72 mm. This represents a minimum return loss of −47.24 dB. A better understanding of both the synthesis parameters and the relationship between structure and electromagnetic properties can open new possibilities for applications and the development of microwave absorbing materials.

FeCl₃∙6H₂O was used as raw material to produce Fe₃O₄, using the solvothermal method with ethylene glycol as the solvent. Fe₃O₄, with different particle sizes, was obtained via mechanical ball-milling by controlling the milling time. Effect of the milling time on the structure, morphology, and electromagnetic parameters of Fe₃O₄ were studied, and the absorption properties and mechanism of Fe₃O₄, for different milling times were analyzed. The results showed that the integrity of the original small spherical structure decreased as the ball milling time increased. Fe₃O₄ showed excellent microwave absorptions as the milling time reached 2 h, the reflection loss reached the maximum of −21.19 dB at 4.64 GHz as the thickness was 6.55 mm.

Hollow magnetic structures have great potential to be used in the microwave absorbing field. Herein, Fe₃O₄ hollow spheres with different levels of hollowness were synthesized by the hydrothermal method under Ostwald ripening effect. In addition to their microstructures, the microwave absorption properties of such spheres were investigated. The results show that the grain size and hollowness of Fe₃O₄ hollow spheres both increase as the reaction time increases. With increasing hollowness, the attenuation ability of electromagnetic wave of Fe₃O₄ spheres increases first and then decreases, finally increases sharply after the spheres break down. Samples with strong attenuation ability can achieve good impedance matching, which it does preferentially as the absorber thickness increases. Fe₃O₄ hollow spheres show the best microwave absorption performance when the reaction time is 24 h. The minimum reflection loss (R_{L (min)}) can reach −40 dB, while the thickness is only 3.2 mm.