Electronic Structures, Magnetism, and Phonon Spectra in the Metallic Cubic Perovskite BaOsO3

TL;DR

This study uses ab initio calculations to explore the electronic, magnetic, and phonon properties of cubic BaOsO3 and related compounds, revealing the delicate balance between spin-orbit coupling, Coulomb interactions, and structural effects.

Contribution

It provides new insights into how spin-orbit coupling and structural distortions influence magnetism and phonon stability in BaOsO3 and related perovskites.

Findings

BaOsO3 is nonmagnetic due to strong SOC but can become magnetic with Coulomb interactions.

CaOsO3's ground state is magnetically ordered due to reduced SOC from structural distortion.

Unstable phonon modes are found in BaOsO3 and BaRuO3, indicating potential structural instabilities.

Abstract

Using ab initio calculations, we have investigated a cubic perovskite BaOsO3 and a few related compounds that have been synthesized recently and formally have a metallic d^4 configuration. In BaOsO3, which shows obvious 3-dimensional fermiology, a nonmagnetism is induced by a large spin-orbit coupling (SOC), which is precisely equal to an exchange splitting ~0.4 eV of the $t_{2g}$ manifold. However, the inclusion of on-site Coulomb repulsion as small as $U^c$~1.2 eV, only 1/3 of the $t_{2g}$ bandwidth, leads to the emergence of a spin-ordered moment, indicating that this system is on the verge of magnetism. In contrast to BaOsO3, our calculations suggest that the ground state of an orthorhombic CaOsO3 is a magnetically ordered state due to the reduction of the strength of SOC (about a half of that of BaOsO3) driven by the structure distortion, although the magnetization energy is only a few tenths of meV. Furthermore, in the cubic BaOsO3 and BaRuO3, our full-phonon calculations show several unstable modes, requiring further research.