First principles calculations of the magnetic and hyperfine properties of Fe/N/Fe and Fe/O/Fe multilayers in the ground state of cohesive energy

• EF=Etot−∑xnExi where Exi is the total energy of each atom making the compound.
• Ecoh=Etot−∑xnExatomo; EtotEtot is total energy, Exatomo is the energy free state.
• Hyperfine interactions are interactions between atomic nuclei and electric charges.
• The electric field gradient (EFG) is highly sensitive to the electronic density in the immediate vicinity of a nucleus.
• The isomer shift (IS) provides important information about the nuclear structure and the physical and chemical environment of atoms.

The ground state properties of Fe/N/Fe and Fe/O/Fe multilayers were investigated using the first principles calculations. The calculations were performed using the Linearized Augmented Plane Wave (LAPW) method implemented in the Wien2k code. A supercell consisting of one layer of nitride (or oxide) between two layers of Fe in the bcc structure was used to model the structure of the multilayer. The research in new materials also stimulated theoretical and experimental studies of iron-based nitrides due to their variety of structural and magnetic properties for the potential applications as in high strength steels and for high corrosion resistance. It is obvious from many reports that magnetic iron nitrides such as γ-Fe4N and α-Fe16N2 have interesting magnetic properties, among these a high magnetisation saturation and a high density crimp. However, although Fe–N films and multilayers have many potential applications, they can be produced in many ways and are being extensively studied from the theoretical point of view there is no detailed knowledge of their electronic structure. Clearly, efforts to understand the influence of the nitrogen atoms on the entire electronic structure are needed as to correctly interpret the observed changes in the magnetic properties when going from Fe–N bulk compounds to multilayer structures.Nevertheless, the N atoms are not solely responsible for electronics alterations in solid compounds. Theoretical results showed that Fe4X bulk compounds, where X is a variable atom with increasing atomic number (Z), the nature of bonding between X and adjacent Fe atoms changes from more covalent to more ionic and the magnetic moments of Fe also increase for Z=7, i.e. N. This is an indicative that atoms with a Z number higher than 7, i.e., O, can produce several new alterations in the entire magnetic properties of Fe multilayers.This paper presents the first results of an ab-initio electronic structure calculations, performed for Fe–N and Fe–O multilayers. Firstly, the formation energy and the cohesive energy of the multilayers are discussed. For optimised values, the cohesive energy of the multilayers to obtain the lattice parameters at the equilibrium ground state was used, i.e. a new methodology for this calculus was applied. Secondly, the magnetic properties and hyperfine interactions (magnetic field, electric field gradient and the isomer shift) of the iron atoms of the multilayers are discussed.