Spin crossover in FeO under shock compression

TL;DR

This study uses shock compression and in situ X-ray techniques to investigate the spin state of iron in FeO at extreme pressures, revealing a continuous spin crossover that persists beyond Earth's core conditions, informing planetary interior models.

Contribution

First experimental observation of continuous iron spin crossover in FeO at pressures up to 900 GPa using shock compression and in situ X-ray methods.

Findings

FeO exhibits a continuous spin crossover under high pressure.

High-spin state persists beyond Earth's core-mantle boundary conditions.

Provides new constraints for planetary interior models.

Abstract

FeO (w\"ustite), which exhibits complex electronic and structural properties with increasing pressure and temperature, is a key mineralogical phase for understanding deep planetary interiors. However, direct measurements of its spin state at high-pressure and temperature remain challenging in static compression experiments. Here, we employ laser-driven shock compression to extend the FeO principal Hugoniot up to $\sim$900 GPa and perform in situ X-ray diffraction and X-ray emission spectroscopy up to 250 GPa, probing FeO's crystal structure and spin state. We demonstrate a continuous spin crossover of iron in FeO over a broad pressure range, with the high-spin state persisting beyond Earth's core-mantle boundary (CMB) conditions. These observations provide new experimental constraints on iron spin state at extreme conditions essential for geophysical models of (exo)planetary interiors.