First-principles prediction of enhanced magnetic anisotropy of a”-phase Fe16N2 with B and C impurities

Intrinsic magnetic properties and uniaxial magnetic anisotropy ( $K_{u}$ ) of $\alpha ''$ -phase ordered Fe16N2– x B x and Fe16N2– x C x alloys have been investigated through first-principles calculations. Being in agreement with experimental results, the lattice parameters, magnetic moments, and $K_{u}$ of $\alpha ''$ -Fe16N2 have been determined. Small addition of B or C dopant atoms enhances tetragonal distortion and $K_{u}$ up to 0.75 MJ $\cdot \text{m}^{-3}$ for both Fe16N1.75B0.25 and Fe16N1.75C0.25 compounds, which is more than 20% larger compared with that (0.6 MJ $\cdot \text{m}^{-3}$ ) of $\alpha ''$ -Fe16N2. Furthermore, the presence of B and C reduces magnetic moments of its neighboring Fe atoms at the 4e and 8h sites, resulting in reduced magnetization, due to less electron transfer from Fe to B and C than N. The underlying mechanism for the enhancement in $K_{u}$ is discussed in connection with the Jahn–Teller lattice distortion, atom-decomposed magnetocrystalline anisotropy, and orbital magnetism.