RESUMO
The microwave properties of epoxy composites filled with 30 wt.% of BaFe12-xGaxO19 (0.1 ≤ x ≤ 1.2) and with 1 wt.% of multi-walled carbon nanotubes (CNTs) were investigated in the frequency range 36-55 GHz. A sufficient increase in the microwave shielding efficiency was found for ternary 1 wt.%CNT/30 wt.% BaFe12-xGaxO19/epoxy composites compared with binary 1% CNT/epoxy and 30 wt.% BaFe12-xGaxO19/epoxy due to the complementary contributions of dielectric and magnetic losses. Thus, the addition of only 1 wt.% of CNTs along with 30 wt.% of barium hexaferrite into epoxy resin increased the frequency range where electromagnetic radiation is intensely attenuated. A correlation between the cation Ga3+ concentration in the BaFe12-xGaxO19 filler and amplitude-frequency characteristics of the natural ferromagnetic resonance (NFMR) in 1 wt.%CNT/30 wt.% BaFe12-xGaxO19/epoxy composites was determined. Higher values of the resonance frequency fres (51.8-52.4 GHz) and weaker dependence of fres on the Ga3+ concentration were observed compared with pressed polycrystalline BaFe12-xGaxO19 (fres = 49.6-50.4 GHz). An increase in the NFMR amplitude on the applied magnetic field for both random and aligned 1 wt.% CNT/30 wt.% BaFe12-xGaxO19/epoxy composites was found. The frequency of NFMR was approximately constant in the range of the applied magnetic field, H = 0-5 kOe, for the random 1 wt.% CNT/30 wt.% BaFe12-xGaxO19/epoxy composite, and it slightly increased for the aligned 1 wt.% CNT/30 wt.% BaFe12-xGaxO19/epoxy composite.
RESUMO
The paper describes preparation features of functional composites based on ferrites, such as "Ba(Fe1-xGax)12O19/epoxy," and the results of studying their systems; namely, the correlation between structure, magnetic properties and electromagnetic absorption characteristics. We demonstrated the strong mutual influence of the chemical compositions of magnetic fillers (Ba(Fe1-xGax)12O19 0.01 < x < 0.1 solid solutions), and the main magnetic (coercivity, magnetization, anisotropy field and the first anisotropy constant) and microwave (resonant frequency and amplitude) characteristics of functional composites with 30 wt.% of hexaferrite. The paper presents a correlation between the chemical compositions of composites and amplitude-frequency characteristics. Increase of Ga-content from x = 0 to 0.1 in Ba(Fe1-xGax)12O19/epoxy composites leads to increase of the resonant frequency from 51 to 54 GHz and absorption amplitude from -1.5 to -10.5 dB/mm. The ability to control the electromagnetic properties in these types of composites opens great prospects for their practical applications due to high absorption efficiency, and lower cost in comparison with pure ceramics oxides.