Thermoelectric power at low temperatures in Ce(Ni_1-xPd _x)₂Ge₂ and CeCu_5.9Au_0.1 in the vicinity of antiferromagnetic quantum critical point

We present experimental results of thermoelectric power S and magnetic specific heat C_m down to 0.2 K for Ce(Ni_1-xPd _x)₂Ge₂ (x = 0 ∼ 0.12) and CeCu _5.9Au_0.1, being located in the vicinity of antiferromagnetic quantum critical point (AFM-QCP). S/T for Ce(Ni _1-xPd_x)₂Ge₂ shows complicated temperature dependence in contrast to a monotonic increase in the C _m/T with decreasing temperatures. The correlation parameter q, equivalent to the ratio S/C_m, decreases below 10 K attaining a considerably smaller value than unity at the lowest temperature for CeNi ₂Ge₂. On the other hand, the q for CeCu _5.9Au_0.1 deviates upward below 0.6 K from the saturation around 1 K, and reaches unity at the lowest temperature. The contrastive observation in the q between the both systems at low temperatures seems to reflect the difference in the AFM-QCP type.