###### Abstract  
To create materials that interact effectively with electromagnetic (EM) radiation, new nanosized substituted ferrites (NiZn)\({}_{1-x}\)Mn\({}_{x}\)Fe\({}_{2}\)O\({}_{4}\) (x = 0, 0.5, and 1) anchored on the surface of multi-walled carbon nanotubes (CNTs) have been synthesized. The concentration of CNTs in the (NiZn)\({}_{1-x}\)Mn\({}_{x}\)Fe\({}_{2}\)O\({}_{4}\)/CNT system was from 0.05 to 0.07 vol. fractions. The dielectric and magnetic characteristics of both pristine (NiZn)\({}_{1-x}\)Mn\({}_{x}\)Fe\({}_{2}\)O\({}_{4}\) ferrites and (NiZn)\({}_{1-x}\)Mn\({}_{x}\)Fe\({}_{2}\)O\({}_{4}\)/CNT composite systems were studied. The introduction of (NiZn)\({}_{1-x}\)Mn\({}_{x}\)Fe\({}_{2}\)O\({}_{4}\)/CNT composites into the amorphous epoxy matrix allows to tailor absorbing properties at the high-frequency by effectively shifting the maximum peak values of the absorption and reflection coefficient to a region of lower frequencies (20-30 GHz). The microwave adsorption properties of (NiZn)\({}_{1-x}\)Mn\({}_{x}\)Fe\({}_{2}\)O\({}_{4}\)/0.07 CNT-ER (x = 0.5) systems showed that the maximum absorption bandwidth with reflection loss below \(-\)10 dB is about 11 GHz. nanosized spinel ferrites; carbon nanotubes; polymer matrix systems; absorption coefficient; reflection loss +
Footnote †: journal:The capacity of a material to absorb electromagnetic radiation hinges on its electrical and magnetic properties, which encompass electrical conductivity and, dielectric and magnetic permeability. These characteristics play a pivotal role in analyzing the process of EM wave propagation, and they are typically nonlinear, tensor, and complex quantities. When EMR interacts with an absorbing material, processes such as reflection, absorption, multiple scattering (due to the structural and geometric inhomogeneity of the material), and wave interference come into play. The absorption of electromagnetic energy occurs due to dielectric, magnetic, and conduction losses, which tend to be maximized to achieve optimal shielding efficiency. Simultaneously, when electromagnetic waves strike a material, reflection occurs at the interface between the media. A greater discrepancy between the wave impedances of the media results in a higher reflection coefficient [8]. The primary objective in the development of absorbing materials is to align the absorbing structure with the surrounding space, minimizing the integral effect of reflection. Considering the operating principles, absorbent materials can be categorized into interference (utilizing the principle of mutual damping of electromagnetic waves by superimposing incident and reflected waves in antiphase), dissipating (reducing reflected energy by scattering it in other directions at various angles), absorbing (transforming an electromagnetic wave into other types of energy, typically thermal, due to dielectric and magnetic material losses), and combined (combining different principles of action) [9]. Maintaining a balance between the dielectric and magnetic characteristics of nanomaterials is crucial for the efficient absorption of electromagnetic waves that penetrate the material deeply. This balance is essential since absorption is facilitated by the interaction of electric and magnetic dipoles with external electromagnetic fields, matching with the impedance of the environment. Thus, to enhance the absorption loss of interfering electromagnetic waves, absorbent materials must exhibit appropriate conductivity, dielectric permittivity, and permeability. Nowadays polymer composite materials based on various polymer matrices filled with carbon materials (carbon nanotubes, graphene nanoplatelets, carbon fibers, graphite) are actively investigated and gain considerable interest as electromagnetic interference (EMI) shielding materials [8; 10; 11; 12; 13; 14]. Electron conducting materials can serve as a shield to minimise or even eliminate interference phenomena by primarily reflecting electromagnetic waves.