BaFe12−xZrxO19 with Zr4+ at 4f1 and 2b sites exhibits an RL of ∼−40 dB and bandwidth of ∼10 GHz at ∼0.8 mm around the millimeter wavelength atmospheric window of 35 GHz.
Ti-doped barium ferrite powders BaFe12−xTixO19 (x = 0, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8) were synthesized by the sol–gel method. The phase structure and morphology were analyzed by x-ray diffraction (XRD) and scanning electron microscopy, respectively. The powders were also studied for their magnetic properties and microwave absorption. Results show that the Ti-doped barium ferrites (BFTO) exist in single phase and exhibit hexagonal plate-like structure. The anisotropy field Ha of the BFTO decreases almost linearly with the increase in Ti concentration, which leads to a shift of the natural resonance peak toward low frequency. Two natural resonance peaks appear, which can be assigned to the double values of the Landé factor g that are found to be ∼2.0 and ∼2.3 in the system and can be essentially attributed to the existence of Fe3+ ions and the exchange coupling effect between Fe3+ and Fe2+ ions, respectively. Such a dual resonance effect contributes a broad magnetic loss peak and thus a high attenuation constant, and leads to a dual reflection loss (RL) peak over the frequency range between 26.5 and 40 GHz. The high attenuation constants are between 350 and 500 at peak position. The optimal RL reaches around −45 dB and the practicable frequency bandwidth is beyond 11 GHz. This suggests that the BFTO powders could be used as microwave absorbing materials with extraordinary properties.
Multiferroic ceramics with extraordinary susceptibilities coexisting are vitally important for the multi-functionality and integration of electronic devices. However, multiferroic composites, as the most potential candidates, will introduce inevitable interface deficiencies and thus dielectric loss from dissimilar phases. In this study, single-phased ferrite ceramics with considerable magnetic and dielectric performances appearing simultaneously were fabricated by doping target ions in higher valence than that of Fe3+, such as Ti4+, Nb5+ and Zr4+, into BaFe12O19. In terms of charge balance, Fe3+/Fe2+ pair dipoles are produced through the substitution of Fe3+ by high-valenced ions. The electron hopping between Fe3+ and Fe2+ ions results in colossal permittivity. Whilst the single-phased ceramics doped by target ions exhibit low dielectric loss naturally due to the diminishment of interfacial polarization and still maintain typical magnetic properties. This study provides a convenient method to attain practicable materials with both outstanding magnetic and dielectric properties, which may be of interest to integration and multi-functionality of electronic devices.
BaFe12−2xNbxNixO19 transforms into a potential soft magnetic material and its excellent absorption properties with a broad bandwidth cover a wide range of <18 to >40 GHz with x varying from 0 to 0.8.
The development of high-efficiency
microwave absorbers for C and
X bands still remains a challenge, limiting the settlement of corresponding
electromagnetic pollution and radar stealth. In this work, a reduced
graphene oxide (RGO)/Cu/Fe3O4 composite is successfully
proposed by a one-step solvothermal method with a GO dispersion content
of 5 mL, where Fe3O4 exhibits high magnetic
loss from natural resonance at the C band, and Cu nanorods and RGO
are introduced as dual conductive phases to produce suitable dielectric
properties by regulating the percolation threshold. The results show
that the existence of Cu nanorods significantly reduces the conductivity
and dielectric loss of the composites, optimizing the coordination
of attenuation capacity and impedance matching in the C and X bands.
Consequently, the obtained RGO/Cu/Fe3O4 composite
shows outstanding microwave absorption performance with the maximum
effective absorption bandwidth (EAB) value of 5.2 GHz at a thin thickness
of 3.1 mm, which covers 84% of the C band and 46% of the X band (4.64–9.84
GHz). The performance is superior to the vast majority of previous
absorbers in the corresponding bands.
BaFe12−xNbxO19 (BFNO, x=0‐0.6) powders with Nb5+ substituting for Fe3+ were prepared by sol‐gel method. The formation process and electromagnetic (EM) wave absorption properties of the BFNO are investigated in detail. With Nb5+ content increasing from x=0 to x=0.6, the formation temperature of barium ferrite phase without heat time increases from ~700°C to ~900°C, while the appearance temperature of typical plate grains decreases from ~1300°C to ~1100°C, and the crystallization ability decreases at 600°C‐900°C, while the grain size increases gradually at 1100°C‐1300°C. Increasing sintering temperature and time promote the formation of barium ferrite phase and grain growth in all the samples. The ε′ and ε″ of the sample with x=0.6 sintered at 1300°C for 3 hours reach highest of ~7.9 and ~0.95 over 26.5‐40 GHz. Multiresonance peaks in permeability decrease from 40+ GHz to ~30 GHz with x rising from 0 to 0.6. Ultimately, small RLmin of ~−42 dB, thin dm of ~0.76 mm, and broad bandwidth of >12 GHz can be exhibited simultaneously around millimeter wave atmospheric window of 35 GHz.
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