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

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) BaRuO3. While the 3C variant of BaRuO3 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 BaRuO3 in the 3C and 4H structures. Our study reveals that the difference in connectivity of RuO6 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.