Metal-Carbon Nanocomposites FeNi/C: Production, Phase Composition, Magnetic Properties

FeNi alloy nanoparticles as a part of metal-carbon nanocomposites were obtained. The synthesis was carried out under conditions of IR annealing of precursors based on joint solution of polyvinyl alcohol (PVA) and hydrates of iron and nickel nitrates. The features of formation of FeNi nanoparticles as a function of the synthesis conditions, as well as the effect of the synthesis temperature and the structure and composition of nanocomposites on their magnetic properties, were studied. It has been established that FeNi alloy nanoparticles can be formed in two ways simultaneously: through the reduction of nanoparticles of nickel-substituted magnetite (Ni, Fe) Fe2O4 and the reduction of Fe2O3 to iron, which dissolves in nickel or Ni3Fe. The average size of the alloy nanoparticles increases from 6 to 14 nm, the size distribution range widens, and its maximum shifts from 3–5 to 9–11 nm as the synthesis temperature increases to 700°C. The growth of nanoparticles occurs owing to agglomeration processes caused by structural changes in the nanocomposite matrix during IR heating. It has been shown that the materials obtained at temperatures above 400°C exhibit ferromagnetic properties and at T = 700°C exhibit properties characteristic of nanosized particles of a solid solution of FeNi. The growth of nanoparticles as the synthesis temperature rises and reduction of iron oxides leads to the increase in saturation magnetization. Changes in the coercive force are determined by an increase in the average size of FeNi nanoparticles with increasing synthesis temperature. So for nanocomposites synthesized at 600°C, the coercive force is maximal, and then a secondary decrease occurs owing to the formation of larger nanoparticles.