PRESSURE EFFECTS ON THE YB VALENCE STATE IN YBIN1-XAGXCU4(X = 0-0.2)

Magnetic susceptibility and electrical resistivity of the YbIn1-xAgxCu4(x less-than-or-equal-to 0.2) system were measured as a function of pressure and temperature. The result shows that the valence phase transition temperature, T(v) decreases with increasing pressure at a rate of -1.7 K/kbar for x = 0, -1.8 K/kbar for x = 0.1 and -1.9 K/kbar for x = 0.2. The pressure dependence of T(v) for x = 0 is similar to that reported previously in non-stoichiometric Yb1-yInyCu2, with the exception that the transition is extremely sharp in our sample. In addition to the decrease in T(v), the magnetic susceptibility above T(v) for x = 0.2 is found to increase slightly with increasing pressure. This increment can be regarded as a pressure effect on the Weiss temperature from the Curie-Weiss fittings. The change in the Weiss temperature is interpreted due to the pressure induced enhancement of c-f hybridization.