Microstructure, Magnetic and Mossbauer Studies of Mechanically Alloyed FeCoNi Nanocrystalline Powders

Magnetic structures have attracted a great interest due to their multiple applications, from physics to biomedicine. Iron, nickel and cobalt are among the most important ferromagnetic elements, therefore the synthesis of Fe-based alloys processed by ball milling from the Fe, Ni and Co powders is of particular interest. This subject mainly concerned the structural and magnetic properties evolution of Fe50Co25Ni25 nanocrystalline powder mixture prepared by mechanical alloying in a high-energy planetary ball mill under argon atmosphere. For extended milling time of 100 h, two nanocrystalline Fe (Co,Ni) (similar to 87 nm) and fcc-Co-rich (similar to 47 nm) phases were identified. This phase transformations, dependent on the alloying time, are related to the increase in dislocations and accumulation of stacking faults. Dislocation density of 1.25 x 10(15) m(-2) is estimated after 100 h of milling. The milled FeCoNi alloy displays a soft ferromagnetic behavior with single magnetic domain (Hc similar to 12.5 Oe and Mr/Ms similar to 0.007 for 100 h milling). Mossbauer analysis gives three main magnetic components: two different components attributed to metallic Fe species located in bcc and fcc Fe-Co-Ni domains and a magnetic component characterized by larger hyperfine fields and isomer shifts typical of Fe3+, Fe2+ species and Fe ions.