In the last decade, the development of new materials that absorb electromagnetic radiation (EMR) has received research interest as they can significantly enhance the performance of electronic devices and prevent adverse effects caused by electromagnetic pollution. Electromagnetic radiation absorbers with a low weight and small thickness of the absorber layer, good absorption capacity, and a wide frequency response bandwidth are highly demanded. Here, for the first time, the properties of polymer nanocomposites FeCoCr/C synthesized by doping FeCoCr alloy nanoparticles into a polymer matrix of pyrolyzed polyacrylonitrile are investigated. An analysis of the magnetic properties of FeCoCr/C nanocomposites showed that increasing the synthesis temperature increased the specific magnetization and coercive force values of the FeCoCr/C nanocomposites. The dependence between the ratio of metals in the precursor of pyrolyzed polyacrylonitrile and the electromagnetic and wave-absorbing properties of FeCoCr/C nanocomposites is considered, and the results of complex dielectric and magnetic permeability measurements are analyzed. It is found that the most promising of all the studied materials are those obtained at T = 700 °C with the ratio of metals Fe:Co:Cr = 35:35:30.

New materials are actively being developed for use in various fields of electronics, as they can significantly improve the performance of electronic devices and prevent adverse effects. Such materials include nanocomposites, which include nanoparticles of magnetic metals and alloys in a non-magnetic polymer or carbon matrix. For the first time, we synthesized FeCoSm/C nanocomposites and studied the effect of synthesis conditions on their structure, composition, and electromagnetic properties. Thermogravimetric (TG) analysis and differential scanning calorimetry (DSC) analysis of the heating processes of nanocomposite precursors allowed optimizing the mode of IR processing of precursors. X-ray phase analysis (XPA) showed that nanoparticles of a solid-metal solution based on the FeCo structure are formed, and at temperatures above 700 °C, the formation of SmCo5-x alloy nanoparticles is also possible. As the synthesis temperature increases, the average size of nanoparticles of alloys containing Sm increases. The effect of the metal ratio in the precursor on the structure, composition, and electromagnetic properties of FeCoSm/C nanocomposites is analyzed. It has been established that the most promising of all the studied materials are those obtained at a temperature of 700 °C with a metal ratio of Fe:Co:Sm = 50:40:10.