Effect of geometry on magnetism of Hund's metals: A case study with BaRuO$_3$

TL;DR

This study investigates how structural geometry influences magnetism in BaRuO$_3$, revealing that connectivity differences lead to distinct magnetic behaviors, with potential to induce antiferromagnetic metallic states through parameter tuning.

Contribution

The paper combines density-functional theory and dynamical mean-field theory to elucidate how octahedral connectivity affects magnetic properties in different BaRuO$_3$ phases, highlighting the role of covalency and Coulomb interactions.

Findings

3C phase is ferromagnetic below 60K.

4H phase exhibits paramagnetism with antiferromagnetic correlations.

Adjusting Coulomb parameters could stabilize antiferromagnetic order.

Abstract

In order to explore the effects of structural geometry on properties of correlated metals we investigate the magnetic properties of cubic (3C) and hexagonal (4H) BaRuO$_3$. While the 3C variant of BaRuO$_3$ is ferromagnetic below 60K, the 4H phase does not show any long-range magnetic order, however, 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 BaRuO$_3$ in the 3C and 4H structures. Our study reveals that the difference in connectivity of 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.