Synthesis, thermal stability, magnetic properties, and microwave absorption applications of CoNi-C core-shell nanoparticles with tunable Co/Ni molar ratio

Magnetic alloy-C core-shell nanoparticles with tunable elemental components are highly expected for their controllable magnetic, catalytic, and electromagnetic properties, and high air stability. Here we present a simple one-step metal organic chemical vapor deposition for the synthesis of CoNi-C core-shell nanoparticles with tunable Co/Ni molar ratio. The as-synthesized nanoparticles have core sizes of 5–50 nm, shell thicknesses of ~5 nm, and tunable Co/Ni molar ratio determined by the molar ratio of Co(acac)3/Ni(acac)2 used in the precursor. The core-shell nanoparticles are very stable in ambient atmosphere at the temperature below 200 °C, and exhibit a slight oxidation in the temperature range of 200–400 °C. The core-shell nanoparticles with Co/Ni molar ratios of 1.27:1, 0.64:1, and 0.30:1 exhibit saturation magnetization values of 41, 31, and 24 emu/g, and coercivity values of 483, 346, and 362 Oe, respectively. It is demonstrated that the microwave absorption parameters of the as-synthesized nanoparticles can be tuned by the Co/Ni molar ratio, which provides a practical strategy to regulate the microwave absorption properties of nanostructured absorbers.