Morphology and magnetic properties of α”-Fe₁₆N₂ nanoparticles synthesized from iron hydroxide and iron oxides

抄録

  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. H_c and H_k^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.