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

Abstract The introduction of an oxidation treatment to the synthesis of spherical and core–shell α″-Fe 16 N 2 /Al 2 O 3 nanoparticles (~62 nm) from plasma-synthesized core–shell α-Fe/Al 2 O 3 nanoparticles has been found to result in a high yield of α″-Fe 16 N 2 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 NH 3 gases during the hydrogen reduction and nitridation steps. The saturation magnetization and magnetic coercivity of the core–shell α″-Fe 16 N 2 /Al 2 O 3 magnetic nanoparticles were found to be 156 emu/g and 1450 Oe, respectively. The detailed effects of the oxidation on the formation of α″-Fe 16 N 2 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.