Morphology and magnetic properties of α”-Fe 16 N 2 nanoparticles synthesized from iron hydroxide and iron oxides

Abstract

Metastable α"-Fe16N2 have attracted much interest as a candidate for rare-earth-free hard magnetic materials. To realize high coercivity, it is necessary to utilize not only the magnetocrystalline anisotropy but also the shape anisotropy of α"-Fe16N2 nanoparticles assemblies. An increase in magnetostatic couplings and intergranular exchange couplings among particles typically reduces the coercivity. Therefore, it is very important to evaluate the anisotropy and magnetic interactions among α"-Fe16N2 nanoparticles. We have examined the changes in morphology, structure and magnetic properties through the synthesis of α"-Fe16N2 nanoparticles from various materials such as α-FeOOH, ɤ-Fe2O3, and Fe3O4. The magnetic interactions were also estimated based on experimental results obtained by analysis of the rotational hysteresis loss of randomly oriented nanoparticles. Hc and Hk ptc for the α"-Fe16N2 nanoparticle assemblies for different starting materials ranged from 2.2 to 1.1 kOe, and from 11 to 12 kOe respectively. Experimental results of the normalized coercive force and normalized switching field suggests that the existence of large magnetic interactions among α"-Fe16N2 nanoparticles.