Fe-based Ternary Magnetic Nitrides are Negative Charge Transfer Compounds

Nitrides display unique chemical and structural characteristics rendering them attractive for a wide variety of applications that complement those of oxides. However, limited by the inherent stability of dinitrogen and competition with oxide formation, only a small number of transition metal ternary nitrides are known. To this end, we employ first-principles calculations to study the magnetic and electronic properties of a ternary iron nitrides with Fe³⁺ d⁵ electronic configurations. We examine the electronic structure in detail and explain how σ- and π-bonding interactions contribute to the stability of various antiferromagnetic insulating and potentially metallic phases. Our density functional theory (DFT) results suggest the ternary iron nitrides are proximate to the negative charge transfer insulator-metal boundary owing to the strong local π-donor character of the N^3- to Fe³⁺. This material family may offer a promising new materials platform for exploring Mott and Slater metal-insulator transitions.