Pressure-induced high-spin/low-spin disproportionated state in the Mott insulator FeBO3

Abstract

The pressure-induced Mott insulator-to-metal transitions are often accompanied by a collapse of magnetic interactions associated with delocalization of 3d electrons and high-spin to low-spin (HS-LS) state transition. Here, we address a long-standing controversy regarding the high-pressure behavior of an archetypal Mott insulator FeBO3 and show the insufficiency of a standard theoretical approach assuming a conventional HS-LS transition for the description of the electronic properties of the Mott insulators at high pressures. Using high-resolution x-ray diffraction measurements supplemented by Mössbauer spectroscopy up to pressures ~ 150 GPa, we document an unusual electronic state characterized by a “mixed” HS/LS state with a stable abundance ratio realized in the $$R\overline{3 }c$$ R 3 ¯ c crystal structure with a single Fe site within a wide pressure range of ~ 50–106 GPa. Our results imply an unconventional cooperative (and probably dynamical) nature of the ordering of the HS/LS Fe sites randomly distributed over the lattice, resulting in frustration of magnetic moments.

Fe0.79Si0.07B0.14 metallic glass gaskets for high-pressure research beyond 1 Mbar

“…If the gasket would have been made entirely of Re or W, the diffraction lines of these strongly scattering materials would overlap with the diffraction spots of the single crystal substantially reducing the quality of the data. Here we focus on a single pressure point of 103.3 (1) GPa as the full data have been recently published (Xu et al, 2022).…”

Orthogonal magnetic structures of Fe4O5: representation analysis and DFT calculations

“…Interestingly, both doublet and singlet components have rather low centre shift values of −0.30 mm s −1 and 0.34 mm s −1 , respectively, unambiguously identifying them as low-spin state iron ions. 4,[42][43][44][45] The further pressure increase to 60 GPa (Fig. 6c) results in the increase of the relative abundance of the doublet and singlet components to 19.7% and 8.4%, respectively, which, combined, equals the amount of iron at the Fe1 site.…”

Temperature- and Field-Induced Transformation of the Magnetic State in Co2.5Ge0.5BO5

“…Transition-metal borates are gaining increasing attention due to the extraordinary magnetic, optical, and electronic properties resulting from the strong interrelation between the lattice, electronic, and spin degrees of freedom. Along with magnetic transitions, these materials demonstrate charge- and orbital orderings, metal–insulator transitions, and spin crossovers under the action of temperature, magnetic field, or external pressure. − The high thermal and chemical stability, a relatively high laser damage threshold, and wide transparent regions make borates promising second-order nonlinear optical materials (NLO) . Borates are also important for applications, due to their high predicted electrical capacity and tunable voltage. − …”