Iron Nitride Family at Reduced Dimensions: A Review of Their Synthesis Protocols and Structural and Magnetic Properties

Magnetic nanoparticles (NPs) are prominent in various fields of scientific research and applications such as magnetic energy storage, magnetic fluids, biomedical fields, and catalysis. Metallic Fe NPs are difficult to protect from air oxidation, and iron oxide NPs suffer from reduced magnetization. Iron nitrides have the advantage of retaining high saturation magnetization (MS); for example, α″-Fe16N2 and γ′-Fe4N have average magnetic moments of 2.9 and 2 μB/Fe, respectively, which are comparable to 2.2 μB/Fe for α-Fe. The iron nitrides are ferromagnetic (FM) up to a maximum lattice dilution of 25% nitrogen for ε-Fe3N. Even though Fe–N NPs are extremely attractive as magnetic materials, the focus has been majorly on the bulk powders and thin films. This review provides a comprehensive overview of the crystal structures, nitriding kinetics, and synthesis methodologies of binary, doped, and ternary nanostructures, thin films, and bulk materials and their magnetism. Substitution of Fe by any other metal atom in the doped and ternary nanostructures breaks the long-range FM ordering but equally provides interesting low-temperature magnetic ordering such as spin glass and exchange bias. The dopant concentration dependence of the magnetic properties of the hybrid systems is discussed.