The 6H-Perovskite Dimer Lattice with Antiferromagnetic Interactions: Ba$_3$ARu$_2$O$_9$

TL;DR

This study combines theoretical and experimental methods to analyze the magnetic properties of the 6H-perovskite Ba$_3$Zn$_{1-x}$Ca$_x$Ru$_2$O$_9$, revealing a transition from nonmagnetic to magnetic states driven by interdimer couplings and identifying mechanisms for magnetic moment suppression.

Contribution

It introduces a comprehensive framework combining mean-field, spin-wave theory, DFT, and neutron scattering to understand magnetic behavior in 6H-perovskite dimers, highlighting mechanisms for moment suppression.

Findings

Phase diagram showing transition from nonmagnetic to magnetic ground states.

Identification of three mechanisms for magnetic moment suppression.

Quantitative agreement with experimental data through combined theoretical and neutron scattering analysis.

Abstract

We investigate the magnetic behavior of the 6H-perovskite dimer lattice Ba$_3$Zn$_{1-x}$Ca$_x$Ru$_2$O$_9$ using analytical theory, density functional theory, inelastic neutron scattering, and modeling of historical magnetization and neutron-scattering data. A dimer mean-field theory built upon classical Luttinger-Tisza analysis generates a phase diagram revealing a transition from a nonmagnetic singlet to a finite-moment ground state as interdimer couplings increase. A (generalized) linear spin-wave theory captures multiplet mixing, excitation gap closing, and fluctuation-induced moment suppression. Density functional theory on select compounds and neutron spectroscopy on dilute Ba$_3$Zn(Ru$_{1-x}$Sb$_x$)$_2$O$_9$ confirm the exchange hierarchy, enabling quantification of previously published experiments within this framework. Our results identify three mechanisms for magnetic moment suppression: quantum fluctuations, ligand hybridization, and nonmagnetic-singlet/magnetic-multiplet mixing.