Interplay of Chemical Bonding and Magnetism in Fe_4N, Fe_3N, Fe_2N

TL;DR

This study uses spin density functional theory to analyze the chemical bonding and magnetic properties of Fe-N compounds, revealing covalent Fe-N bonds and their influence on magnetic moments across different phases.

Contribution

It provides a detailed comparative analysis of bonding and magnetism in Fe_4N, Fe_3N, and Fe_2N, highlighting the role of covalent bonds and exchange splitting in their magnetic behavior.

Findings

Strong covalent Fe-N bonds due to p-d hybridization.

Magnetic moments decrease in steps of 0.5 μ_B across the compounds.

Majority spin d bands are fully occupied, minority are near half-filling.

Abstract

Using spin density functional theory we have carried out a comparative study of chemical bonding and magnetism in Fe_4N, Fe_3N and Fe_2N. All of these compounds form close packed Fe lattices, while N occupies octahedral interstitial positions. High spin fcc Fe and hypothetical FeN with rock salt structure have been included in our study as reference systems. We find strong, covalent Fe-N bonds as a result of a substantial \sigma-type p-d hybridisation, with some charge transfer to N. Those Fe d orbitals which contribute to the p-d bonds, do no longer participate in the exchange splitting of the Fe d bands. Because of the large exchange fields, the majority spin d bands are always fully occupied, while the minority spin d bands are close to half-filling, thus optimizing the Fe d-d covalent bonding. As a consequence, in good approximation the individual Fe moments decrease in steps of 0.5 \mu_B from fcc iron (2.7 \mu_B) via Fe_4N (2.7 and 1.97 mu_B}), \chem{Fe_3N} (1.99 \mu_B) to \zeta - Fe_2N (1.43 \mu_B).