Electronic properties of transition-metal oxides under high pressure revealed by x-rayemission spectroscopy

Abstract

The high-pressure electronic and magnetic properties of MnO, CoO and NiO have beeninvestigated by x-ray emission spectroscopy. Both MnO and CoO show a magneticcollapse revealed by the abrupt decrease of the satellite intensity in the metalK β emission lines at about 80 and 100 GPa respectively. The magnetic transition pressuresagree well with the known structural transition pressures in these systems. No suchmagnetic transition was observed in NiO, which rather shows hints of delocalization of thed electrons. The NiO data have been further analysed within a full multiplet approach. Thelow- and high-pressure emission spectra could be reproduced well. The confrontationbetween theory and experiment gives a handle on fundamental quantities such as theelectron correlation strength, hybridization and charge transfer energy, introduced in thecalculations as parameters. Both theoretical and experimental clues indicate that NiO is onthe verge of a metal–insulator transition. In MnO and CoO, the magnetic transition islikely to arise from the interplay between the ligand field and the O p bandwidth.