Spin states of iron impurities in magnesium oxide under pressure: A possible intermediate state

TL;DR

This study uses first-principles calculations to explore the spin states of iron impurities in magnesium oxide under pressure, revealing a metastable intermediate spin state that could impact understanding Earth's lower mantle.

Contribution

It provides the first detailed theoretical analysis of iron impurity spin states in MgO under pressure, including the identification of a metastable intermediate spin state.

Findings

Identification of a metastable intermediate spin state (S=1) in neutral iron impurities.

Analysis of electronic and magnetic properties across different spin and charge states.

Extension of results to high-pressure conditions relevant to Earth's mantle.

Abstract

Ferropericlase (Mg,Fe)O is a major lower mantle mineral, and studying its properties is a fundamental step toward understanding the Earth's interior. Here, we performed a first-principles investigation on the properties of iron as an isolated impurity in magnesium oxide, which is the condition of ferropericlase under which iron-iron interactions could be neglected. The calculations were carried using the all-electron full-potential linearized augmented plane wave method within the density functional theory in the generalized gradient approximation plus the on-site Hubbard correction. We present the electronic and magnetic properties, electric and magnetic hyperfine splitting of this impurity in high and low spin states for several charge states at zero pressure, which were then extended to high pressures. For the impurity in the neutral charge state, our results indicated that there is a metastable intermediate spin state (S=1), in addition to the high (S=2) and low (S=0) spin states. Those results were discussed in the context of an intermediate spin state, experimentally identified in ferrosilicate perovskite.