Effect of geometry on magnetism of Hund's metals: Case study of BaRuO3

Abstract

In order to explore the effects of structural geometry on the properties of correlated metals we investigate the magnetic properties of cubic ($3C$) and hexagonal ($4H$) ${\mathrm{BaRuO}}_{3}$. While the $3C$ variant of ${\mathrm{BaRuO}}_{3}$ is ferromagnetic below 60 K, the $4H$ phase does not show any long-range magnetic order, though, there is experimental evidence of short-range antiferromagnetic correlations. Employing a combination of computational tools, namely, density-functional theory and dynamical mean-field theory calculations, we probe the origin of contrasting magnetic properties of ${\mathrm{BaRuO}}_{3}$ in the $3C$ and $4H$ structures. Our study reveals that the difference in connectivity of ${\mathrm{RuO}}_{6}$ octahedra in the two phases results in different Ru-O covalency, which in turn influences substantially the strengths of screened interaction values for Hubbard $U$ and Hund's rule $J$. With estimated $U$ and $J$ values, the $3C$ phase turns out to be a ferromagnetic metal, while the $4H$ phase shows paramagnetic behavior with vanishing ordered moments. However, this paramagnetic phase bears signatures of antiferromagnetic correlations, as confirmed by a calculation of the magnetic susceptibility. We find that the $4H$ phase is found to be at the verge of antiferromagnetic long-range order, which can be stabilized upon slight changes of screened Coulomb parameters $U$ and $J$, opening up the possibility of achieving a rare example of an antiferromagnetic metal.