Low field ac-susceptibility experiments have been carried out to study the effect of “chemical” disorder and proximity to a magnetic quantum critical point (QCP) on the non-Fermi liquid (NFL) behavior in $\mathrm{Ce}{\left({\mathrm{Ru}}_{1-x}{\mathrm{Rh}}_x\right)}_2{\mathrm{Si}}_2$ for $x=0.5$ and 0.6 and $\mathrm{Ce}{\mathrm{Cu}}_{5.9}{\mathrm{Au}}_{0.1}$. The susceptibility of strongly disordered NFL material $\mathrm{Ce}{\left({\mathrm{Ru}}_{1-x}{\mathrm{Rh}}_x\right)}_2{\mathrm{Si}}_2$ contains two components associated with different mechanisms; a disorder-driven component $\delta \chi$ and a mean-field (MF) quantum critical component ${\chi }_{\mathrm{MF}}$. $\delta \chi$ exhibits $H∕T$-scaling in the form of $T^{-\gamma }f(H∕T)$ with $\gamma$ depending on $x$. In contrast, the disorder-driven component has not been observed in weakly disordered NFL material $\mathrm{Ce}{\mathrm{Cu}}_{5.9}{\mathrm{Au}}_{0.1}$. The results of the scaling analysis strongly suggest that $\delta \chi$ is due to the quantum Griffiths singularity.

• Received 17 December 2003

DOI:https://doi.org/10.1103/PhysRevB.70.144415