Electromagnetic Properties of Carbon Nanotube/BaFe12-xGaxO19/Epoxy Composites with Random and Oriented Filler Distributions

Abstract

The microwave properties of epoxy composites filled with 30 wt.% of BaFe_12-xGa_xO₁₉ (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.% BaFe_12-xGa_xO₁₉/epoxy composites compared with binary 1% CNT/epoxy and 30 wt.% BaFe_12-xGa_xO₁₉/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 BaFe_12-xGa_xO₁₉ filler and amplitude-frequency characteristics of the natural ferromagnetic resonance (NFMR) in 1 wt.%CNT/30 wt.% BaFe_12-xGa_xO₁₉/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 BaFe_12-xGa_xO₁₉ (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.% BaFe_12-xGa_xO₁₉/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.% BaFe_12-xGa_xO₁₉/epoxy composite, and it slightly increased for the aligned 1 wt.% CNT/30 wt.% BaFe_12-xGa_xO₁₉/epoxy composite.

Keywords: carbon-based magnetodielectric nanocomposites; doped M-type hexaferrites; microwave properties; natural ferromagnetic resonance; resonance frequency.