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

• Published in: Journal of magnetism and magnetic materials Vol. 381; pp. 89 - 98
• Main Authors: Zulhijah, Rizka, Nandiyanto, Asep Bayu Dani, Ogi, Takashi, Iwaki, Toru, Nakamura, Keitaro, Okuyama, Kikuo
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.05.2015
• Subjects: Maghemite; Nitridation process; Oxidation treatment; Plasma; α-Fe; α”-Fe16N2; Plasma; Oxidation treatment; Nitridation process; α”-Fe16N2; α-Fe; Maghemite
• ISSN: 0304-8853
• DOI: 10.1016/j.jmmm.2014.12.015

The introduction of an oxidation treatment to the synthesis of spherical and core–shell α″-Fe16N2/Al2O3 nanoparticles (~62nm) from plasma-synthesized core–shell α-Fe/Al2O3 nanoparticles has been found to result in a high yield of α″-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 H2 and NH3 gases during the hydrogen reduction and nitridation steps. The saturation magnetization and magnetic coercivity of the core–shell α″-Fe16N2/Al2O3 magnetic nanoparticles were found to be 156emu/g and 1450Oe, respectively. The detailed effects of the oxidation on the formation of α″-Fe16N2 phase were investigated by characterizing the morphology (SEM, TEM and BET), elemental composition (EDX, EELS, and XAFS) and magnetic properties (Mössbauer and MSPS) of the prepared particles. The good magnetic properties obtained have the potential for future applications such as rare-earth-free magnetic materials. •High yield of α″-Fe16N2 up to 98% was prepared from core–shell α-Fe/Al2O3 NPs.•Introduction of oxidation improved yield of α″-Fe16N2 for large size of NPs.•Oxidation forming microporous structured maghemite facilitated nitridation process.•Particle morphology changed during the nitrogen process due to atomic dislocation.•Core–shell α″-Fe16N2/Al2O3 nanoparticles showed good magnetic performances.