Effects of Ni content on nanocrystalline Fe–Co–Ni ternary alloys synthesized by a chemical reduction method

• We prepared nanocrystalline Fe–Co–Ni alloys by a novel chemical reduction process.
• Elemental compositions could be well controlled by the molar ratio of metal sources.
• Particle size and magnetic properties clearly depended on the Ni contents.
• Fe50Co10Ni40 exhibited high saturation magnetization of 126.3 emu/g.

Magnetic properties of Fe–Co–Ni ternary alloys could be altered by changing of the particle size, elemental compositions, and crystalline structures. In this work, Fe50Co50−xNix nanoparticles (x=10, 20, 40, and 50) were prepared by the novel chemical reduction process. Hydrazine monohydrate was used as a reducing agent under the concentrated basic condition with the presence of poly(vinylpyrrolidone). We found that the nanoparticles were composed of Fe, Co and Ni with compositions according to the molar ratio of the metal sources. Interestingly, the particles were well-crystalline at the as-prepared state without post-annealing at high temperature. Increasing Ni content resulted in phase transformation from body centered cubic (bcc) to face centered cubic (fcc). For the fcc phase, the average particle size decreased when increased the Ni content; the Fe50Ni50 nanoparticles had the smallest average size with the narrowest size distribution. In additions, the particles exhibited ferromagnetic properties at room temperature with the coercivities higher than 300 Oe, and the saturation magnetiation decreased with increasing Ni content. These results suggest that the structural and magnetic properties of Fe–Co–Ni alloys could be adjusted by varying the Ni content.