Facile Synthesis of High Magnetization Air-stable Fe65Co35 Nanoparticles by Mechanical Alloying

Fe65Co35 nanoparticles were prepared by mechanical alloying of the elemental Fe and Co powders in air. The structural, morphology, and magnetic property variations were investigated as a function of milling time (in the 0.25–32 h range) by using xray diffraction, scanning electron microscopy, and vibrating sample magnetometry. The complete formation of bcc Fe65Co35 solid solution was observed after 10 h milling. At this time, the alloy powder with average grain size (crystallite size) of 12 nm and a maximum saturation magnetization (Ms) 200 emu/g was obtained. Intensive milling of Fe-Co powders resulted in a grain refinement down below 10 nm and in reduction of Ms to 170 emu/g. The saturation magnetization of the alloys asmilled for various milling times was almost unchanged, at least after seven days of storing in air, which suggests a formation of certain oxide layer on particles surface to protect them from further oxidation. The annealing of as-milled sample at 800C under gas mixture of hydrogen and argon affected in a strong increase of Ms, from 170 emu/g to 220 emu/g, that supports the above hypothesis on the existence of the oxide layer.