Fragility of the magnetic order in the prototypical altermagnet RuO$_2$

TL;DR

This paper investigates the magnetic properties of RuO$_2$, revealing that its magnetism depends on Ru vacancies and that electronic correlations are weak, which may explain conflicting experimental observations.

Contribution

It demonstrates that RuO$_2$'s magnetism is sensitive to Ru vacancies and that a smaller Hubbard U suffices to describe its electronic structure, clarifying previous controversies.

Findings

RuO$_2$'s electronic properties are described with a smaller Hubbard U than needed for magnetism.

Ru vacancies can promote magnetic ordering in RuO$_2$.

Characterizing Ru vacancy levels could resolve experimental discrepancies.

Abstract

Altermagnetism is a topic that has lately been gaining attention and the RuO$_2$ compound is among one of the most studied altermagnetic candidates. However, the survey of available literature on RuO$_2$ properties suggests that there is no consensus about the magnetism of this material. By performing density functional theory calculations, we show that the electronic properties of stoichiometric RuO$_2$ are described in terms of a smaller Hubbard $U$ within DFT+$U$ than the value required to have magnetism. We further argue that Ru vacancies can actually aid the formation of a magnetic state in RuO$_2$. This in turn suggests that a characterization of the amount of Ru vacancies in experimental samples might help the resolution of the controversy between the different experimental results.