Magnetic Moment and Anisotropy of Iron Nitride Fe16N2 Nanoparticles

We report on the magnetic properties of highly homogeneous Fe16N2 nanoparticles prepared by an ammonia nitrification method. Mossbauer spectroscopy experiments revealed the large hyperfine field characteristic of Fe16N2. TEM observation showed that the particles are covered with oxide shells. The saturation magnetization and the coercive force are 108 emu/g and 3450 Oe, respectively. The angle dependence of the MH curves for the magnetically aligned samples indicates that the magnetic interaction between the particles is negligibly small, suggesting that the magnetocrystalline anisotropy is significantly large. Under the assumption that only the ferromagnetic core is responsible for magnetization, the magnetization and the anisotropy constant of the core Fe16N2 powders were estimated as 196±10 emu/g of Fe and K fpU1 =4.1 ± 0.4 x 106 erg/cm3, respectively.