Complex electronic, magnetic, and structural transformations in FeO

Iron oxides are important materials for Geoscience but also for basic science and applied technologies [1, 2]. Iron monoxide is likely to be the final constituent of the evolution of subducted banded iron formations and might be a source of the low-velocity zones at the Earth’s core-mantle boundary [3]. The stability and high-pressure properties of Fex O could, thus, determine the fate of banded iron formations and their potential role in processes in Earth and planetary interiors, including controls on redox cycles. Fex O transforms from B1 structure into rhombohedral distorted-B1 phase (rB1) at about 16 GPa, which correlates with a transition from the paramagnetic state to the state with the antiferromagnetic order [4]. A further transition from the rB1 phase to a hexagonal B8 phase has been proposed at 74 GPa and 900 K [5]. Although numerous studies were focused on the investigation of the electronic and magnetic properties and phase diagram of Fex O, information on the Fe2+/Fe3+ interplay, magnetic and structural coupling of Fex O at high pressures and high temperature are very limited, e.g. he pressure dependence of the Néel temperature of Fex O was determined only up to 40 GPa under non-hydrostatic conditions [4]. We will present our investigation on the pressure dependence of the electronic, magnetic and structural properties of Fex O by means of Synchrotron Mössbauer Source spectroscopy and Single-Crystal X-ray diffraction in resistively- and laserheated diamond anvil cells. We will discuss the interplay between Fe2+ and Fe3+ and its effects on the magnetic properties of Fex O and their potential role in the mineralogy, chemistry, and physics of the Earth’s deep interior.