Synthesis of Fe-Co nanoparticles with high saturation magnetization by low-temperature post-annealing

Fe-Co nanoparticles were synthesized by the thermal decomposition of a mixed precursor of Fe(CO)(5) and Co-2(CO)(8). As-synthesized Fe-Co nanoparticles formed clusters 20 nm in diameter consisting of many primary 5-nm nanoparticles. The saturation magnetization of as-synthesized Fe-Co nanoparticles was about 140 emu/g(net). This was only 60% of the saturation magnetization of bulk Fe70Co30, due to the presence of a surfactant and the small grain size within the primary nanoparticles of less than 20 nm. During post-annealing at 250 degrees C, the primary NPs sintered, and the nanoparticle clusters grew into a single crystal by atomic diffusion. As a result, the saturation magnetization reached a maximum of 212 emu/g(net) for Fe : Co = 68 : 32, and varied with chemical composition in a relationship similar to the Slater-Pauling curve. (C) 2012 American Institute of Physics. [doi:10.1063/1.3679027]