Magnetocrystalline anisotropy energies of Fe16N2 and Fe16C2

The magnetocrystalline anisotropy energy (MAE) of Fe16N2 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 Fe16N2 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 mu(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 Fe16C2 becomes negative for the same E-x as for Fe16N2. Taking E-x = 0.1110 Ry, the calculated magenetic moment for Fe16C2 qualitatively agrees with the experimental result for the disordered-state alpha'-Fe-C. (c) 2006 Elsevier B.V. All rights reserved.