## 4 Conclusions  
Nano-sized (NiZn)\({}_{1-\mathrm{x}}\)Mn\({}_{\mathrm{x}}\)Fe\({}_{2}\)O\({}_{4}\) ferrites (x = 0, 0.5, and 1) and (NiZn)\({}_{1-\mathrm{x}}\)Mn\({}_{\mathrm{x}}\)Fe\({}_{2}\)O\({}_{4}\)/CNT nanocomposites were synthesized through a one-pot co-precipitation process. The concentration of carbon nanotubes (CNTs) in the (NiZn)\({}_{1-\mathrm{x}}\)Mn\({}_{\mathrm{x}}\)Fe\({}_{2}\)O\({}_{4}\)/CNT system ranged from 0.05 to 0.07 vol. fractions, and the particle size of substituted ferrites on the surface of carbon nanotubes was within the range of 5-20 nm. An increase in the concentration of CNTs in (NiZn)\({}_{1-\mathrm{x}}\)Mn\({}_{\mathrm{x}}\)Fe\({}_{2}\)O\({}_{4}\)/CNT composites led to elevated values of \(\epsilon^{\prime}\) and \(\epsilon^{\prime\prime}\) for all values of x. The (NiZn)\({}_{1-\mathrm{x}}\)Mn\({}_{\mathrm{x}}\)Fe\({}_{2}\)O\({}_{4}\)/CNT nanocomposites exhibited conductivity at a frequency of 100 Hz approximately 2-3 orders of magnitude higher than that observed for (NiZn)\({}_{1-\mathrm{x}}\)Mn\({}_{\mathrm{x}}\)Fe\({}_{2}\)O\({}_{4}\) ferrites. In the frequency range of 12 GHz to 20 GHz, the electromagnetic wave absorption processes in nanocomposites based on carbon nanotubes decorated with substituted ferrites were more efficient, demonstrating good impedance matching characteristics. Additionally, the absorption coefficient of electromagnetic waves in the frequency range of 15-25 GHz for (NiZn)\({}_{1-\mathrm{x}}\)Mn\({}_{\mathrm{x}}\)Fe\({}_{2}\)O\({}_{4}\)/0.07 CNT (x = 0, 0.5, and 1) nanocomposites was up to 1.5 times higher than that for unmodified substituted ferrites. Polymer-based systems incorporating (NiZn)\({}_{1-\mathrm{x}}\)Mn\({}_{\mathrm{x}}\)Fe\({}_{2}\)O\({}_{4}\)/CNT nanostructures were constructed using amorphous epoxy resin as a matrix. As the filler volume content increased in the epoxy matrix for (NiZn)\({}_{1-\mathrm{x}}\)Mn\({}_{\mathrm{x}}\)Fe\({}_{2}\)O\({}_{4}\)/0.07 CNT-ER systems with different ion doping (x = 0, 0.5, and 1), there was a rise in the maximum peak values of the absorp \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Absorber/Matrix** & **Minimum** & **Frequency of** & **Sample Thickness** & **Bandwidth of** & \\  & \(RL\) (dB) & **Minimum RL (GHz)** & **d (mm)** & \(RL<-10\) dB (GHz)** & **Ref.** \\ \hline Ni\({}_{0.6}\)Zn\({}_{0.4}\)Fe\({}_{2}\)O\({}_{4}\)/epoxy resin & \(-37.47\) & 12.60 & 3.1 & 9.00 & [44] \\ CNT (2.5 wt. \%)—epoxy resin & \(-17.00\) & 9.30 & 2.0 & 2.10 & [45] \\ Ce\({}_{2}\)O\({}_{4}\)—MWCNT (2 wt. \%)—epoxy resin & \(-28.00\) & 9.00 & 3.0 & 4.00 & [46] \\ SeFe\({}_{7.5}\)Co\({}_{12}\)Ti\({}_{12}\)O\({}_{9}\)/epoxy resin & \(-42.00\) & 6.30 & 4.0 & 4.00 & [20] \\ Ge (4.77 vol. \%)—epoxy resin & \(-23.83\) & 8.40 & 4.0 & 10.8 & [47] \\ Ni\({}_{2}\)Fe\({}_{2}\)O\({}_{9}\)/Fe\({}_{2}\)O\({}_{4}\)/0.07 CNT-ER & \(-16.40\) & 28.93 & 2.5 & 9.46 & This work \\ Ni\({}_{0.25}\)Zn\({}_{0.25}\)Mn\({}_{0.5}\)Fe\({}_{2}\)O\({}_{4}\)/0.07 CNT-ER & \(-15.41\) & 29.96 & 2.5 & 10.55 & This work \\ MnFe\({}_{2}\)O\({}_{4}\)/0.07 CNT-ER & \(-18.8\) & 30.01 & 2.5 & 10.62 & This work \\ (CNT = 0.0025 vol. \%) & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The microwave absorption properties of polymer composite materials reported in literature compared with experimental data. tion coefficient, and these maxima shifted toward lower frequency region. All polymer composites with a filler content of 0.0025 volumetric fraction demonstrated the highest bandwidth (\(RL<-10\) dB). The optimal range of (NiZn)\({}_{1-x}\)Mn\({}_{x}\)Fe\({}_{2}\)O\({}_{4}\)/0.07 CNT filler concentrations, corresponding to the absorption bandwidth with reflection loss below \(-10\) dB for polymer composites, was found to be from 0.005 to 0.0075 vol. fractions. The microwave adsorption properties of (NiZn)\({}_{1-x}\)Mn\({}_{x}\)Fe\({}_{2}\)O\({}_{4}\)/0.07 CNT-ER (x = 0.5) systems indicated that the maximum absorption bandwidth with a reflection loss below \(-10\) dB is about 11 GHz.