We investigate the evolution of the magnetic properties in FeS under pressure and show that these cannot be explained solely in terms of the spin-state transition from a high to low spin state due to an increase of the crystal field. Using a combination of density functional theory and dynamical mean-field theory (DFT+DMFT), our calculations show that at normal conditions the ${\mathrm{Fe}}^{2+}$ ions are in the $3d^6$ high-spin ($S=2$) state, with some admixture of a $3d^7\underline{L}$ ($S=3/2$) configuration, where $\underline{L}$ stands for the ligand hole. Suppressing the magnetic moment by uniform compression is related to a substantial increase in electron delocalization and occupation of several lower spin configurations. The electronic configuration of Fe ions cannot be characterized by a single ionic state, but only by a mixture of the $3d^7\underline{L},3d^8{\underline{L}}^2$, and $3d^9{\underline{L}}^3$ configurations at pressures $\sim 7.5\mathrm{GPa}$. The local spin-spin correlation function shows well-defined local magnetic moment, corresponding to a large lifetime in the high spin state at normal conditions. Under pressure FeS demonstrates a transition to a mixed state with small lifetimes in each of the spin configurations.

• Received 8 August 2016
• Revised 13 March 2017

DOI:https://doi.org/10.1103/PhysRevB.95.205116