Hexagonal $\mathrm{BaIr}{\mathrm{O}}_3$ is a magnetic insulator driven by the spin-orbit interaction (SOI), whereas $\mathrm{BaRu}{\mathrm{O}}_3$ is an enhanced paramagnetic metal. Our investigation of structural, magnetic, transport, and thermal properties reveals that substitution of $\mathrm{R}{\mathrm{u}}^{4+} \left(4d^4\right)$ ions for $\mathrm{I}{\mathrm{r}}^{4+} \left(5d^5\right)$ ions in $\mathrm{BaIr}{\mathrm{O}}_3$ reduces the magnitudes of the SOI and a monoclinic structural distortion and rebalances the competition between the SOI and the lattice degrees of freedom to render an evolution from a magnetic insulting state to a robust metallic state. The central findings of this paper are as follows: (1) light Ru doping $\left(0<x\le 0.15\right)$ prompts simultaneous, precipitous drops in both the magnetic ordering temperature $T_{\mathrm{N}}$ and the electrical resistivity, and (2) heavier Ru doping $\left(0.41\le x\le 0.9\right)$ induces a robust metallic state without any long-range magnetic order. All results suggest a critical role of the lattice degrees of freedom in determining the ground state in the heavy transition-metal oxides.

• Received 9 October 2015
• Revised 23 March 2016

DOI:https://doi.org/10.1103/PhysRevB.93.165136