Magnetic iron nitrides inspired by historic research on α″-Fe16N2

Abstract

Strong ferromagnetic materials at room temperature are of interest for various magnetic applications such as magnetic recording, sensors, and motors. Gigantic magnetism expected for α″-Fe₁₆N₂ thin films had been attracted much attention in terms of its large magnetization per weight in comparison to rare earth iron nitrides R₂Fe₁₇N₃ because these films are made of only iron and nitrogen. It developed much straggling on iron nitride thin film research but inconsistent results were obtained using different preparation methods. A powdered α″-Fe₁₆N₂-like compound was prepared by the ammonolysis of fine α-Fe powder in low temperature below 200 °C to clarify the confusion; the magnetism was not large in α″-Fe₁₆N₂ itself but was increased in the intermediate ammonolysis dual-phase mixture product of the α″-Fe₁₆N₂-like compound and residual α-Fe. A way to control the magnetic coercivity was subsequently investigated to utilize the larger magnetization in the α″-Fe₁₆N₂-like compound mixture as magnetic materials similarly to Sm₂Fe₁₇N₃ bonded magnet. Iron nitrides, zinc blende type γ″-FeN and rock-salt type γ‴-FeN, also decompose at around 500 °C. Thermal decomposition was a disadvantage in the preparation of the iron nitrides; however, iron nanoparticles dispersed composites in AlN matrix were derived from the iron nitrides (Fe,Al)N by thermal treatment including laser heating. Iron nitrides are thus promising magnetic materials for their potential applications in science and technology.