  Iron-based layered systems are of great interest because of their ability to
tune effective material parameters such as magnetic anisotropy energy (MAE).
The influence of the crystallographic structure of Fe, its thickness, and the
presence of other layers above and below the Fe layer on magnetic parameters,
such as the MAE of the studied system, is an intriguing and important topic
from an application point of view. Here, we present a density functional theory
(DFT) study of the magnetic anisotropy of nine-monolayer Fe, FeCo, and FeCo
films with B, C, and N dopants placed in octahedral interstitial positions. The
theoretical study is based on calculations using the full-potential
local-orbital code FPLO and the generalized gradient approximation. The
chemical disorder in the FeCo layers was modeled using the virtual crystal
approximation. The structures of the layers were subjected to optimization of
the geometry of the interlayer spacings and the neighborhood of the dopant
sites. We determined the local magnetic moments and the excess charge at each
layer position. We also identified the influence of dopant atoms on the
magnetic properties of FeCo layers, such as magnetization and magnetic
anisotropy.
