The challenge of unravelling magnetic properties in LaFeAsO

TL;DR

This paper systematically analyzes the magnetic properties of LaFeAsO using multiple first principles methods, revealing the itinerant nature of magnetism and the sensitivity of results to computational details, which complicates understanding its magnetic interactions.

Contribution

It demonstrates that well-converged all-electron calculations are consistent and highlights the itinerant character of magnetism in LaFeAsO, clarifying previous discrepancies.

Findings

Results are highly sensitive to computational details.

Magnetic ground state shows itinerant character with long-range interactions.

Consistent results are obtained with full-potential all-electron methods.

Abstract

First principles calculations of magnetic and, to a lesser extent, electronic properties of the novel LaFeAsO-based superconductors show substantial apparent controversy, as opposed to most weakly or strongly correlated materials. Not only do different reports disagree about quantitative values, there is also a schism in terms of interpreting the basic physics of the magnetic interactions in this system. In this paper, we present a systematic analysis using four different first principles methods and show that while there is an unusual sensitivity to computational details, well-converged full-potential all-electron results are fully consistent among themselves. What makes results so sensitive and the system so different from simple local magnetic moments interacting via basic superexchange mechanisms is the itinerant character of the calculated magnetic ground state, where very soft magnetic moments and long-range interactions are characterized by a particular structure in the reciprocal (as opposed to real) space. Therefore, unravelling the magnetic interactions in their full richness remains a challenging, but utterly important task.