The bulk magnetic susceptibility $\chi (T,B)$ of ${\mathrm{Y}\mathrm{b}\mathrm{R}\mathrm{h}}_2({\mathrm{S}\mathrm{i}}_{0.95}{\mathrm{G}\mathrm{e}}_{0.05}{)}_2$ has been investigated close to the field-induced quantum critical point at $B_c=0.027\mathrm{T}$. For $B\le 0.05\mathrm{T}$ a Curie-Weiss law with a negative Weiss temperature is observed at temperatures below 0.3 K. Outside this region, the susceptibility indicates ferromagnetic quantum critical fluctuations, $\chi (T)\propto T^{-0.6}$ above 0.3 K. At low temperatures the Pauli susceptibility follows ${\chi }_0\propto (B-B_c{)}^{-0.6}$ and scales with the coefficient of the $T^2$ term in the electrical resistivity. The Sommerfeld-Wilson ratio is highly enhanced and increases up to 30 close to the critical field.

• Received 4 September 2004

DOI:https://doi.org/10.1103/PhysRevLett.94.076402