Suppression of ferromagnetism and influence of disorder in silicon-substituted CeRh6Ge4

We report a study of isoelectronic chemical substitution in the recently discovered quantum critical ferromagnet CeRh${}_6$Ge${}_4$. Upon silicon-doping, the ferromagnetic ordering temperature of CeRh${}_6$(Ge${}_{1-x}$Si${}_x$)${}_4$ is continuously suppressed, and no transition is observed beyond $x_c$$\approx$0.125. Non-Fermi liquid behavior with $C\mathrm{/}T\propto$log($T^{\ast }\mathrm{/}T$) is observed close to $x_c$, indicating the existence of strong quantum fluctuations, while the $T$-linear behavior observed upon pressurizing the parent compound is absent in the resistivity, which appears to be a consequence of the disorder induced by silicon doping. Our findings provide evidence for the role played by disorder on the unusual ferromagnetic quantum criticality in CeRh${}_6$Ge${}_4$, and provides further evidence for understanding the origin of this behavior.