Synthesis of monodisperse FeCo nanoparticles by reductive salt-matrix annealing

摘要

We report here a novel synthetic method to prepare monodisperse air-stable FeCo nanoparticles with average sizes of 8, 12 and 20 nm. CoFe_2O _4 nanoparticles of different sizes were first synthesized by a chemical solution method. The as-synthesized CoFe_2O_4 nanoparticles were then mixed with ball-milled NaCl powders and heated to 400-500°C in forming gas (Ar 93%+H_2 7%). The salt powder worked as a separating medium that prevents the CoFe_2O_4 nanoparticles from agglomerating during the heat treatment while the forming gas reduces the CoFe_2O_4 nanoparticles to FeCo nanoparticles. Monodisperse FeCo nanoparticles were recovered by dissolving the NaCl in water and subsequently washing with ethanol and acetone. Structural analyses confirmed that FeCo nanoparticles retained the same size as their oxide precursors. The size of the FeCo nanoparticles can be well tuned by controlling the size of the CoFe_2O_4 nanoparticles. The saturation magnetization of FeCo nanoparticles is size dependent and increases with size.