The iron nitridometalates ${\mathrm{Li}}_2\left[\right({\mathrm{Li}}_{1-x}{\mathrm{Fe}}_x^{\mathrm{I}}\left)\mathrm{N}\right]$ display ferromagnetic ordering and spin freezing. Large magnetic moments up to $5.0{\mu }_{\mathrm{B}}/\mathrm{Fe}$ are found in the magnetization. In Mössbauer effect studies huge hyperfine magnetic fields up to 696 kOe are observed at specific Fe sites. These extraordinary fields and moments originate in an unusual ligand field splitting for those Fe species leading [within local spin density approximation (LSDA)] to a localized orbitally degenerate doublet. Including spin-orbit interaction and strong intra-atomic electron correlation $(\mathrm{LDA}+\mathrm{SO}+U)$ gives rise to a large orbital momentum.

• Received 24 October 2001

DOI:https://doi.org/10.1103/PhysRevLett.88.207202