Shell Thickness-Dependent Microwave Absorption of Core–Shell Fe₃O₄@C Composites

Abstract

Core-shell composites, Fe3O4@C, with 500 nm Fe3O4 microspheres as cores have been successfully prepared through in situ polymerization of phenolic resin on the Fe3O4 surface and subsequent high-temperature carbonization. The thickness of carbon shell, from 20 to 70 nm, can be well controlled by modulating the weight ratio of resorcinol and Fe3O4 microspheres. Carbothermic reduction has not been triggered at present conditions, thus the crystalline phase and magnetic property of Fe3O4 micropsheres can be well preserved during the carbonization process. Although carbon shells display amorphous nature, Raman spectra reveal that the presence of Fe3O4 micropsheres can promote their graphitization degree to a certain extent. Coating Fe3O4 microspheres with carbon shells will not only increase the complex permittivity but also improve characteristic impedance, leading to multiple relaxation processes in these composites, thus the microwave absorption properties of these composites are greatly enhanced. Very interestingly, a critical thickness of carbon shells leads to an unusual dielectric behavior of the core-shell structure, which endows these composites with strong reflection loss, especially in the high frequency range. By considering good chemical homogeneity and microwave absorption, we believe the as-fabricated Fe3O4@C composites can be promising candidates as highly effective microwave absorbers.

Dynamic arrays based on magnetically controlled Fe3O4 particles

“…To further reveal the microwave absorption properties of the Fe 3 O 4 composites, the reflection loss R was analyzed by comparing known literature data of Fe 3 O 4 particles [8][9][10] and obtained experimental data. A comparison of the reflection coefficient data presented as spectra is shown in Figure 5.…”

Three-dimensional (3D) α-Fe2O3/polypyrrole (PPy) nanocomposite for effective electromagnetic absorption

“…The synthesized process of α-Fe 2 O 3 /PPy hybrids is schematically illustrated in the The EA ability of material is decided by its complex permittivity (ε = ε ′ − iε ′′ ) and permeability (µ = µ ′ − i µ ′′ ), 19,20 which were measured using a network analyzer aforementioned. The complex permeability of the samples were taken as 1 (µ = 1) due to both the PPy and the α-Fe 2 O 3 are non-magnetic material.…”

Strengthened electromagnetic absorption performance derived from synergistic effect of carbon nanotube hybrid with Co@C beads

“…7.6 GHz. Conventionally, the magnetic loss of magnetic materials mainly derives from hysteresis loss, domain-wall resonance, natural resonance, and eddy current loss [32,41]. The magnetic hysteresis loss stemming from the irreversible magnetization is only generated in a strong magnetic field.…”