First-Principles Prediction of Enhanced Magnetic Anisotropy of α″-Phase Fe₁₆N₂ With B and C Impurities

Intrinsic magnetic properties and uniaxial magnetic anisotropy (K
_u
) of α"-phase ordered Fe
₁₆
N
_2-x
B
_x
and Fe
₁₆
N
_2-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 α"-Fe
₁₆
N
₂
have been determined. Small addition of B or C dopant atoms enhances tetragonal distortion and K
_u
up to 0.75 MJ·m
^-3
for both Fe
₁₆
N
_1.75
B
_0.25
and Fe
₁₆
N
_1.75
C
_0.25
compounds, which is more than 20% larger compared with that (0.6 MJ·m
^-3
) of α"-Fe
₁₆
N
₂
. 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.