Suppression of magnetism under pressure in FeS: A DFT+DMFT study

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 Fe2+ ions are in the 3d6 high-spin (S=2) state, with some admixture of a 3d7L̲ (S=3/2) configuration, where L̲ 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 3d7L̲,3d8L̲2, and 3d9L̲3 configurations at pressures ~7.5GPa. 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.