Metal-ligand interplay in strongly-correlated oxides: a parametrized phase diagram for pressure induced spin transitions

TL;DR

This study explores how high pressure affects the magnetic properties of transition-metal oxides MnO, FeO, CoO, and NiO, revealing the underlying ligand field changes responsible for pressure-induced spin transitions.

Contribution

It provides a parametrized phase diagram linking pressure, ligand field parameters, and spin states in strongly-correlated oxides, offering new insights into their magnetic transitions.

Findings

Magnetism changes significantly under high pressure in MnO, FeO, CoO.

Ligand field parameters correlate with spin state transitions.

NiO remains unaffected by high pressure in the studied range.

Abstract

We investigate the magnetic properties of archetypal transition-metal oxides MnO, FeO, CoO and NiO under very high pressure by x-ray emission spectroscopy at the K\beta line. We observe a strong modification of the magnetism in the megabar range in all the samples except NiO. The results are analyzed within a multiplet approach including charge-transfer effects. The pressure dependence of the emission line is well accounted for by changes of the ligand field acting on the d electrons and allows us to extract parameters like local d-hybridization strength, O-2p bandwidth and ionic crystal field across the magnetic transition. This approach allows a first-hand insight into the mechanism of the pressure induced spin transition.