Magnetic properties of nanocrystalline γ´-Fe4N and ε-Fe3N synthesized by citrate route

Nanocrystalline γ´-Fe₄N and ε-Fe₃N nitrides are synthesized by using a citrate precursor route. The nitridation of α-Fe₂O₃ results in a nitrogen deficient perovskite γ´-Fe₄N phase at 773 K and hexagonal ε-Fe₃N phase at 823 K. The nitride particle is a magnetic cluster consisting of an assembly of crystallites. γ´-Fe₄N is a weak itinerant ferromagnet and the particles exhibit acicular platelet-like morphology. The magnetic moments in ultrafine γ´-Fe₄N and ε-Fe₃N nitride particles are due to spin pairing effects, lattice expansion due to interstitial nitrogens, superparamagnetic behavior, and randomly canted spin structures at the surface. The reduction of magnetization and Curie temperature (T_c ) is attributed to fine particle size effects. In γ-Fe₄ N and ε-Fe₃N, the intermixing of N-2p states with Fe-3d states occurs because of similarities in their density of states, and thus the reduction of unpaired d-electrons results in the lowering of magnetic moments compared to α-Fe. The Mossbauer study of γ´-Fe₄N and ε-Fe₃N nitrides indicate randomly canted spin structures at the surface and corroborates the observed magnetic properties