Effects of Magnetic Field and Pressure on the Valence-Fluctuating Antiferromagnetic Compound EuPt2Si2

The effects of a magnetic field and pressure on the Kondo-like behavior in the valence-fluctuating antiferromagnetic compound EuPt₂Si₂ were studied using single-crystalline samples. The logarithmic temperature dependence of the electrical resistivity, ρ(T) ∝ -ln T, which is reminiscent of the Kondo effect, is robust against the application of a magnetic field. On the other hand, the temperature dependences of ρ(T) and thermoelectric power S(T) change markedly under pressure. In addition, the antiferromagnetically ordered temperature T_N1 = 21 K at ambient pressure decreases gradually and reaches zero at approximately P = 4 GPa. From the comparison of the magnetic properties of EuPt₂Si₂ with those of EuCu₂(Ge_0.4Si_0.6)₂, the observed anomalous features for EuPt₂Si₂ at low temperatures are inferred to be due to a valence fluctuation and/or a valence change of the Eu ions at low temperatures.