Abstract
The shell on the nano-magnetic absorber can prevent oxidation, which is very important for its practical utilization. Generally, the nonmagnetic shell will decrease the integral magnetic loss and thus weaken the electromagnetic absorption. However, maintaining the original absorption properties of the magnetic core is a major challenge. Here, we designed novel and facile CoxFey@C composites by reducing CoxFe3−xO4@phenolic resin (x = 1, 0.5 and 0.25). High saturation magnetization value (Ms) of CoxFey particle, as a core, shows the interesting magnetic loss ability. Meanwhile, the carbon shell may increase the integral dielectric loss. The resulting composite shows excellent electromagnetic absorption properties. For example, at a coating thickness of 2 mm, the RLmin value can reach to −23 dB with an effective frequency range of 7 GHz (11–18 GHz). The mechanisms of the improved microwave absorption properties are discussed.
Highlights
Solving the oxidization problem of magnetic metal has aroused extreme attention in the field of electromagnetic absorption
From equations (1–2), we conclude that a high magnetization value is quite important
We infer that the carbon shell does not influence the crystal structure of CoFe2O4
Summary
Solving the oxidization problem of magnetic metal has aroused extreme attention in the field of electromagnetic absorption. Despite the fact that these magnetic absorbers have achieved fascinating electromagnetic absorption properties, most magnetic metals (i.e.: Fe, Co, Ni) are restricted by the poor chemical stability and convert into nonmagnetic oxide, i.e. α -Fe2O3, Co2O3, etc This process will seriously affect their magnetic properties and magnetic loss ability. The high dielectric loss shell can make up a slight decrease in the magnetic loss Among these absorbers, Fe3O4-based core-structures have been widely studied including Fe3O4@ ZrO216, Fe3O4@TiO217, Fe3O4@SnO218, and Fe3O4@CuSiO319. Other magnetic/dielectric structures have been reported including Fe@SnO220 and Co@ZnO21 These pristine magnetic cores did not show the interesting complex permeability value due to their smaller Ms After introducing the non-magnetic material, the integral magnetic loss ability will further decrease. 4) The electromagnetic absorption properties can be tuned by adjusting the carbon shell thickness Such a composite offers high stability and strong absorption performance. The Co and Fe atomic ratio can be tuned by adjusting the x value in the CoxFe3−xO4
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