Non-collinear magnetism in iron at high pressures

TL;DR

This study uses a first-principles magnetic tight-binding model to explore non-collinear magnetism in high-pressure iron phases, revealing magnetic configurations that improve agreement with experimental data.

Contribution

It introduces a detailed magnetic model for high-pressure iron phases, highlighting the importance of non-collinear magnetism in accurately predicting their properties.

Findings

Non-collinear antiferromagnetic state is lowest energy in hcp iron.

Magnetic states improve equation of state predictions below 50 GPa.

Non-magnetic models poorly match experimental data at high pressures.

Abstract

Using a first principles based, magnetic tight-binding total energy model, the magnetization energy and moments are computed for various ordered spin configurations in the high pressure polymorphs of iron (fcc, or $\gamma$-Fe, and hcp, or $\epsilon$-Fe), as well ferromagnetic bcc iron ($\alpha$-Fe). For hcp, a non-collinear, antiferromagnetic, spin configuration that minimizes unfavorable ferromagnetic nearest neighbor ordering is the lowest energy state and is more stable than non-magnetic $\epsilon$ iron up to about 75 GPa. Accounting for non-collinear magnetism yields better agreement with the experimental equation of state, in contrast to the non-magnetic equation of state, which is in poor agreement with experiment below 50 GPa.