Magnetism in FeO at Megabar Pressures from X-Ray Emission Spectroscopy

We report evidence for a preserved magnetic state in FeO up to 143 GPa at room temperature using high-resolution x-ray emission spectroscopy. This observation is based on the spectral line shape of the Fe $K\beta$ emission line. Up to the highest pressure, FeO remains a magnetic insulator. Combining our results with previous Mössbauer data, we present a new magnetic phase diagram of FeO. Features like a closed-loop $P-T$ antiferromagnetic domain confirm that high-pressure investigations can reveal new physical properties and unexpected phenomena.