Magnetocrystalline anisotropy energies of Fe16N2 and Fe16C2

Abstract The magnetocrystalline anisotropy energy (MAE) of Fe 16 N 2 with a body-centered tetragonal (BCT) structure is calculated using its approximate energy bands, inclusive of the spin–orbit interaction and exchange splitting ( E x ) based on the tight-binding approximation (TBA). Taking E x =0.1093 Ry, the calculated anisotropy constants of Fe 16 N 2 are in agreement with the measured constants, K 1 , K 2 and K 3 , and the average magnetic moment is evaluated to be about 2.3  μ B /Fe atom, which is close to that obtained from the first-principles calculation by Sakuma. In contrast, the estimated unidirectional anisotropy constant K u (= K 1 + K 2 ) for Fe 16 C 2 becomes negative for the same E x as for Fe 16 N 2 . Taking E x =0.1110 Ry, the calculated magenetic moment for Fe 16 C 2 qualitatively agrees with the experimental result for the disordered-state α′ -Fe–C.