First-principles study of the effect of Fe impurities in MgO at geophysically relevant pressures

TL;DR

This study uses first-principles calculations to investigate how Fe impurities affect magnetic transitions in MgO under high pressures relevant to Earth's mantle, revealing the impact of Fe arrangement and concentration.

Contribution

It provides new insights into the pressure-induced magnetic transition of Fe in MgO, highlighting the effects of Fe distribution and concentration on transition pressures and the limitations of SIC-LSD.

Findings

Critical pressure increases with Fe concentration.

Fe atom arrangements significantly influence transition pressure.

The HS-LS transition is confirmed to be first order.

Abstract

The self-interaction corrected local spin density (SIC-LSD) formalism and the standard GGA treatment of the exchange-correlation energy have been applied to study the collapse of the magnetic moment of Fe impurities in MgO. The system Mg_{1-x}Fe_xO is believed to be the second most abundant mineral in the Earth's lower mantle. We confirm the experimentally found increase of the critical pressure upon iron concentration. Our calculations using standard GGA for a fixed Fe concentration show that different arrangements of Fe atoms can remarkably shift the transition pressure of the high spin (HS) to low spin (LS) transition. This could explain the experimentally found broad transition regions. Our results indicate that the HS-LS transition in Mg$_{1-x}Fe_xO is first order. We find that SIC-LSD fails to predict the divalent Fe configuration as the lowest energy configuration and discuss possible reasons for it.