Effect of oxidation on α-Fe16N2 phase formation from plasma-synthesized spherical core-shell α-Fe/Al2O3 nanoparticles

The introduction of an oxidation treatment to the synthesis of spherical and core-shell alpha ''-Fe16N2/Al2O3 nanoparticles (similar to 62 nm) from plasma-synthesized core-shell alpha-Fe/Al2O3 nanoparticles has been found to result in a high yield of alpha ''-Fe16N2 phase of up to 98%. The oxidation treatment leads the formation of a maghemite phase with open channeled structures along the c-axis, facilitating penetration of H-2 and NH3 gases during the hydrogen reduction and nitridation steps. The saturation magnetization and magnetic coercivity of the core-shell alpha ''-Fe16N2/Al2O3 magnetic nanoparticles were found to be 156 emu/g and 1450 Oe, respectively. The detailed effects of the oxidation on the formation of alpha ''-Fe16N2 phase were investigated by characterizing the morphology (SEM, TEM and BET), elemental composition (EDX, EELS, and XAFS) and magnetic properties (Mossbauer and MSPS) of the prepared particles. The good magnetic properties obtained have the potential for future applications such as rare-earth-free magnetic materials. (C) 2014 Elsevier By. All rights reserved.