This paper presents the synthesis of Fe–Co–Ni nanocomposites by chemical precipitation, followed by a reduction process. It was found that the influence of the chemical composition and reduction temperature greatly alters the phase formation, its structures, particle size distribution, and magnetic properties of Fe–Co–Ni nanocomposites. The initial hydroxides of Fe–Co–Ni combinations were prepared by the co-precipitation method from nitrate precursors and precipitated using alkali. The reduction process was carried out by hydrogen in the temperature range of 300–500 °C under isothermal conditions. The nanocomposites had metallic and intermetallic phases with different lattice parameter values due to the increase in Fe content. In this paper, we showed that the values of the magnetic parameters of nanocomposites can be controlled in the ranges of M_S = 7.6–192.5 Am²/kg, M_r = 0.4–39.7 Am²/kg, M_r/M_s = 0.02–0.32, and H_cM = 4.72–60.68 kA/m by regulating the composition and reduction temperature of the Fe–Co–Ni composites. Due to the reduction process, drastic variations in the magnetic features result from the intermetallic and metallic face formation. The variation in magnetic characteristics is guided by the reduction degree, particle size growth, and crystallinity enhancement. Moreover, the reduction of the surface spins fraction of the nanocomposites under their growth induced an increase in the saturation magnetization. This is the first report where the influence of Fe content on the Fe–Co–Ni ternary system phase content and magnetic properties was evaluated. The Fe–Co–Ni ternary nanocomposites obtained by co-precipitation, followed by the hydrogen reduction led to the formation of better magnetic materials for various magnetically coupled device applications.

The kinetic characteristics of the process of synthesis of Ni nanopowder (NP) by the chemical metallurgy method are studied. Nickel NP is obtained by reduction of NiO nanopowder with hydrogen in a tubular furnace at temperatures in the range from 240 to 280°C. Nickel oxide nanopowder is prepared by thermal decomposition of nickel hydroxide Ni(OH)₂ at 300°C, which has been synthesized in advance by chemical precipitation from aqueous solutions of nickel nitrate 10 wt % and alkali NaOH 10 wt % with pH 9 at room temperature. It is found that NiO NP is more readily reduced at temperatures above 250°C. The rate constant of the reduction process at 280°C is about 2.5 times higher than in the case of reduction at 240°C. The duration of the reduction process at 280°C is shorter by a factor of more than two in comparison with the case of reduction at 240°C. Based on the results of calculation of the activation energy of the reduction process from isothermal data, an assumption is made about the kinetically controlled rate-limiting regime of the reduction of NiO NP. It is revealed that Ni nanoparticles obtained by hydrogen reduction of nickel oxide have an average size in the range of 60–120 nm, and each of them is connected to several adjacent particles by necks.