We report our investigations on ${\mathrm{Ag}}_3{\mathrm{LiIr}}_{1.4}{\mathrm{Ru}}_{0.6}{\mathrm{O}}_6$, which results from the Ru substitution in the Kitaev quantum spin-liquid candidate ${\mathrm{Ag}}_3{\mathrm{LiIr}}_2{\mathrm{O}}_6$. It crystallizes in the monoclinic $C2/m$ space group like its parent compound, ${\mathrm{Ag}}_3{\mathrm{LiIr}}_2{\mathrm{O}}_6$. Our susceptibility measurements reveal an effective moment ${\mu }_{\text{eff}}=2.6{\mu }_B$, which is higher than moments of the parent compound and less than that of the Ru analog $\left({\mathrm{Ag}}_3{\mathrm{LiRu}}_2{\mathrm{O}}_6\right)$, suggesting the presence of magnetic ${\mathrm{Ir}}^{4+}$ $(J_{\text{eff}}=1/2)$ and ${\mathrm{Ru}}^{4+}$ $(S=1)$. Bulk magnetic susceptibility suggests long-range order (LRO) at $T\sim 20\mathrm{K}$, whereas no clear signature is present in the heat capacity. Likewise, there is a loss of the ${}^7\mathrm{Li}$ nuclear magnetic resonance (NMR) spectral intensity around $T\sim 20\mathrm{K}$ as expected at the onset of LRO but a complete wipeout is not seen, in contrast to the result in ${\mathrm{Ag}}_3{\mathrm{LiIr}}_2{\mathrm{O}}_6$. There is as well a $T\sim 20\mathrm{K}$ anomaly in the ${}^7\mathrm{Li}$ NMR relaxation rate $1/T_1$ and also a fall in the ${}^7\mathrm{Li}$ NMR shift $K$ with decreasing temperature. These results suggest LRO at $T\sim 20\mathrm{K}$ in ${\mathrm{Ag}}_3{\mathrm{LiIr}}_{1.4}{\mathrm{Ru}}_{0.6}{\mathrm{O}}_6$. However, at low $T$ below 10 K, we observe a power-law variation in magnetic heat capacity $C_m$ and spin-lattice relaxation rate $1/T_1$, temperature-independent ${}^7\mathrm{K}$, temperature-independent muon spin relaxation rate, and no further loss of the ${}^7\mathrm{Li}$ NMR spectral intensity. These results suggest the persistence or stabilization of a quantum spin-liquid-like phase perhaps from a fraction of the sample in ${\mathrm{Ag}}_3{\mathrm{LiIr}}_{1.4}{\mathrm{Ru}}_{0.6}{\mathrm{O}}_6$ below 10 K. Our muon spin relaxation $\left(\mu \mathrm{SR}\right)$ measurements suggest ordering around 20 K, consistent with our other probes. It appears that the main effect of Ru substitution is to shift the LRO to a higher temperature in comparison with ${\mathrm{Ag}}_3{\mathrm{LiIr}}_2{\mathrm{O}}_6$, though there are signatures of a novel phase below about 10 K.

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• Quantum spin liquid
• Muon spin relaxation & rotation
• Nuclear magnetic resonance
• Specific heat measurements