Synthesis and Electromagnetic and Microwave Absorption Properties of Monodispersive Fe₃O₄/α-Fe₂O₃ Composites

Abstract

Fe 3 O 4 /α-F e2 O 3 composites were synthesized by a one-step method. The composition and their performances were modified by adjusting the concentration of Fe 3+ (FeCl 3 •6H 2 O) in the precursor solution, effectively. Compared with single-phase Fe 3 O 4 and Fe 2 O 3 , the effective microwave absorbing ability of Fe 3 O 4 /α-Fe 2 O 3 composites is much widened in the range 1−18 GHz, which could stem from the enhanced dipolar polarization and interfacial polarization due to lattice dislocations at the interface of Fe 3 O 4 /α-Fe 2 O 3 . The minimum reflection loss (RL) of Fe 3 O 4 /α-Fe 2 O 3 composites reaches about −43.1 dB at a thickness of 2.0 mm, with the effective absorption band reaching 3.4 GHz (9.8−13.2 GHz). In the thickness of 1.5−3.2 mm, the width of the RL reaches 9.9 GHz (3.5−13.4 GHz). The results demonstrate that Fe 3 O 4 /α-Fe 2 O 3 composites could be a candidate to be used as absorbers with the microwave absorption band much widened.

Metal‐Organic Framework Derived Hierarchical Co/C@V2O3 Hollow Spheres as a Thin, Lightweight, and High‐Efficiency Electromagnetic Wave Absorber

“…The resonance peaks are observed at approximately 4 GHz in Figure f, which may be related to the natural resonance of the Co nanoparticles. According to the equation f r = γH eff ( γ is the gyromagnetic ratio, and H eff is the effective anisotropy field), the natural resonance frequency is proportional to H eff . The resonance frequencies of the samples appear in the GHz range, whereas the resonance frequency of bulk Co is located in the MHz range, which is due to the enhanced H eff related to the increased surface anisotropy of the Co nanoparticles.…”

Magnetic properties of hematite (α − Fe2O3) nanoparticles synthesized by sol-gel synthesis method: The influence of particle size and particle size distribution

“…As the size of the particles decreases, the magnetic properties of the iron(III) oxides exhibit peculiar properties, which differ from those of bulk counterpart materials, because of nanoscale confinement and surface effects. They have a range of practical applications in different technological areas, such as solar cell, pigment, microwave absorption, catalysis, environ-ment protection, gas sensor, magnetic storage, clinical diagnosis and treatment, etc [31][32][33][34][35][36][37][38][39][40].…”

Two‐step preparation of fly ash‐based composites for microwave absorption

“…20,21 Generally, the real parts of complex permittivity (ε′) and permeability (µ′) stand for the storage abilities of electromagnetic energy, while both of the imaginary parts (ε″ and µ″) represent dissipation capabilities. 22,23 Figure 3 depicts the frequency dependency of ε r and µ r for pure FA and CoFA700. In case of CoFA700, the relatively complex permittivity displays an apparent decline trend, and the corresponding ε′ and ε″ values decrease from 13.37 to 8.72 and 6.68 to 3.19, respectively.…”

“…It is generally true that the magnetic loss results from natural resonance, exchange resonance, and eddy current loss at 2-18 GHz frequency. 22 Moreover, the eddy current loss can be expressed by the equation µ″≈2πμ 0 (µ′) 2 σd 2 f/3, 20 where d is the coating thickness and σ is the electrical conductivity. The variation of µ″(µ′) −2 f −1 value is usually considered as a crucial parameter to evaluate the contribution of eddy current effect.…”