Impurity-induced moment freezing in NaFe${}_x$Ru${}_{1-x}$O${}_2$

We report the impact of magnetic impurity substitution on the quantum disordered magnetic ground state of NaRuO${}_2$. Local $S=5\mathrm{/}2$ moments are introduced into the frustrated triangular lattice of $J_{eff}=1\mathrm{/}2$ Ru moments via Fe-substitution in NaFe${}_x$Ru${}_{1-x}$O${}_2$, and the evolution of the magnetic ground state is reported. Local spin freezing associated with conventional spin glass behavior is observed upon Fe substitution, marking an impurity-induced freezing of the primarily dynamic magnetic ground state in NaRuO${}_2$. Furthermore, local Fe moments induce a Curie-Weiss magnetic behavior in the uniform magnetic susceptibility, and the local moment magnitude is best described by dynamic Ru moments polarized about impurity sites. Our results establish an impurity-doping phenomenology consistent with inherently dynamic moments in NaRuO${}_2$ that are pinned by local magnetic impurities, similar to ``swiss cheese" models of impurity-substituted copper oxides.