Proximity of LaOFeAs to a magnetic instability

TL;DR

This study uses density functional theory to show that undoped LaOFeAs is near a magnetic instability, with its Fe magnetic moment highly sensitive to pressure but relatively unaffected by structural distortions or Fermi surface changes.

Contribution

It provides a detailed theoretical analysis of pressure effects on magnetism in LaOFeAs, highlighting its proximity to magnetic instability and the role of itinerant electrons.

Findings

Fe moment drops by nearly a factor of 3 within ±5 GPa pressure range

Fe moments are highly sensitive to spin arrangement

Fermi surface topology remains stable up to 10 GPa

Abstract

We investigate the effect of external pressure on the Fe magnetic moment in undoped LaOFeAs within the framework of density functional theory and show that this system is close to a magnetic instability: The Fe moment is found to drop by nearly a factor of 3 within a pressure range of $\pm$ 5 GPa around the calculated equilibrium volume. While the Fe moments show an unusually strong sensitivity to the spin arrangement (type of anti-ferromagnetic structure), the low temperature structural distortion is found to have only a minor influence on them. Analysis of the Fermi surface topology and nesting features shows that these properties change very little up to pressures of at least 10 GPa. We discuss the magnetic instability in terms of the itinerancy of this system.