Pressure-induced transitions in FePS$_3$: Structural, magnetic and electronic properties

Abstract

FePS_33 is a prototype van der Waals layered antiferromagnet and a Mott insulator under ambient conditions, which has been recently reported to go through a pressure-induced dimensionality crossover and an insulator-to-metal transition. These transitions also lead to the appearance of a novel magnetic metallic state. To further understand these emergent structural and physical properties, we have performed a first-principles study using van der Waals and Hubbard UU corrected density functional theory including a random structure search. Our computational study attempts to interpret the experimental coexistence of the low- and intermediate-pressure phases and we predict a novel high-pressure phase with distinctive dimensionality and different possible origins of metallicity.

MPX3 van der Waals magnets under pressure (M = Mn, Ni, V, Fe, Co, Cd; X = S, Se)

“…The second transition (HP-I → HP-II) accompanies the breaking of the P-P dimer structure and the formation of interlayer Pchain perpendicular to the Fe layers, in addition to a sudden collapse of the interlayer distance and volume, (Haines et al, 2018) similar to the case of MnPS 3 . Harms et al (2020) note that these observations are consistent with separate first-principles electronic structure calculation results, (Zheng et al, 2019;Deng et al, 2023) where the origin of the coexistence of the LP and HP-I phases around 2-5 GPa is suggested to be the result of the shear-induced energy barrier between the LP and HP-I phases (see Figure 7A), (Deng et al, 2023). Crystal and magnetic structures of the low-pressure (HP-0) and the first high-pressure (HP-I) phases of FePS 3 .…”

“…Interestingly, on the other hand, a high-pressure neutron diffraction data by Coak et al (2021) suggests the presence of short-range magnetic order in the HP-II phase, persisting even up to room temperature (see Figure 6C, 7B). From a detailed electronic structure calculation study, Deng et al (2023) argues that this puzzling behavior may be explained by the potential coexistence of two metastable metallic states; the high-spin one with the intralayer P 2 dimer structure remains intact comparing the short-range order (2D-like), while the P 2 dimer breaks to form the out-of-plane P chain structure (3D-like) in the other low-spin state. A separate dynamical mean-field theory study on FePS 3 also suggests the coexistence of the two structural phases, each one hosting the normal Fermi liquid-like character (with the interlayer P-chain) and the incoherent "Hund's metal" character (with the intralayer P-dimer) in the high-pressure regime, where the Hund's metal phase keeps the local moments intact and induces badmetallic behavior due to magnetic fluctuations (Kim et al, 2022).…”