Orbital order and magnetism of FeNCN

TL;DR

This study uses density functional calculations to explore the orbital order and magnetic interactions in FeNCN, revealing weak coupling between spin and orbital degrees of freedom and identifying the ground-state orbital configuration.

Contribution

It provides the first detailed microscopic magnetic model and orbital configuration analysis for FeNCN based on first-principles calculations.

Findings

Ground state features doubly occupied d_{3z^2-r^2} orbital

Exchange couplings match experimental data

Alternative orbital configurations are higher in energy by 75 meV/f.u.

Abstract

Based on density functional calculations, we report on the orbital order and microscopic magnetic model of FeNCN, a prototype compound for orbital-only models. Despite having a similar energy scale, the spin and orbital degrees of freedom in FeNCN are only weakly coupled. The ground-state configuration features the doubly occupied d_{3z^2-r^2} (a1g) orbital and four singly-occupied d orbitals resulting in the spin S=2 on the Fe+2 atoms, whereas alternative (Eg') configurations are about 75 meV/f.u. higher in energy. Calculated exchange couplings and band gap are in good agreement with the available experimental data. Experimental effects arising from possible orbital excitations are discussed.