Synthesis and Electromagnetic Properties of FeCoNi/C Nanocomposites Based on Polyvinyl Alcohol

Triple FeCoNi nanoparticles, distributed and stabilized in the carbon matrix of FeCoNi/C metal-carbon nanocomposites, are synthesized. The nanocomposites are synthesized by the method of controlled IR pyrolysis of precursors of the polymer-metal nitrate type obtained by the joint dissolution of the components followed by removal of the solvent. The effect of the synthesis temperature on the structure, composition, and electromagnetic properties of nanocomposites is investigated. It is shown by XRD that the formation of ternary FeCoNi nanoparticles occurs due to the dissolution of Fe in the nanoparticles of a NiCo solid solution. With an increase in the synthesis temperature, the size of metal nanoparticles increases, which is determined by the processes of their agglomeration and coalescence during the matrix rearrangement. Also, depending on the synthesis temperature, nanoparticles of a ternary alloy with different compositions can be formed, and the ratio of metals specified in the precursor is achieved at 700°C. It is shown by Raman spectroscopy that with an increase in the synthesis temperature, the degree of crystallinity of the carbon matrix of nanocomposites increases, and graphene structures consisting of several layers can be formed. The frequency dependences of the relative complex dielectric and magnetic permeability of nanocomposites in the 3–13 GHz range are investigated. It is shown that an increase in the synthesis temperature leads to a significant increase in both dielectric and magnetic losses (by a factor of ~2). The former are related to the formation of a complex nanostructure of the carbon matrix of the nanocomposite, while the latter are determined by an increase in the size of nanoparticles and a shift in the natural ferromagnetic resonance (NFMR) frequency to the low-frequency region. Reflection loss (RL) calculations are carried out according to the standard technique based on experimental data on the frequency dependences of the permeability and permittivity. It is shown that the frequency range and the magnitude of the absorption of electromagnetic waves (from 50 to 94%) can be regulated by changing the temperature of the synthesis of nanocomposites.