First-principles study on the effects of atomic configuration on the magnetic anisotropy energy of (Fe,Co)16(N,C)2 alloys

Abstract

Herein, the first-principles technique combined with a coherent potential approximation is utilized to investigate the magnetic anisotropy energy (MAE) of (Fe1-xCox)16(N,C)2 alloys. The alloys contain an ordered α″-phase and partially ordered α′-phase, where α-Fe is distorted to form a bct structure with c/a = 1.1 owing to the random intrusion of (N, C) atoms. For the α″-phase, the MAE is sensitive to Co substitution sites and reaches approximately 3 MJ/m3 at an x of 0.25 when Co atoms occupy the 4d sites. For the α′-phase, the lattice distortion c/a = 1.1 alone cannot provide a positive MAE when x = 0 (FeN0.125 and FeC0.125). Evidently, both Co substitution and further increasing the c/a over 1.1 must be performed to realize a positive MAE in the α'-phase. Finally, the importance of local distortion of the (Fe, Co) lattice in further increasing the c/a beyond 1.1 is discussed as it increases the effective c/a even when the global c/a is fixed at 1.1.