Ferromagnetic quantum critical fluctuations in YbRh2(Si0.95Ge0.05)2 -: art. no. 076402

The bulk magnetic susceptibility chi(T,B) of YbRh2 (Si0.95Ge0.05)(2) has been investigated close to the field-induced quantum critical point at B-c = 0.027 T. For B less than or equal to 0.05 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) proportional to T-0.6 above 0.3 K. At low temperatures the Pauli susceptibility follows chi(0) proportional to(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.