Effect of pressure on thermopower of EuNi2Ge2

EuNi2Ge2 is antiferromagnetic below TN ≍ 30 K with an effective moment µeff ≍ 7.7 μB, indicating the 4f7 electron configuration (Eu2+) in the ground state. In order to investigate the electronic state of EuNi2Ge2, we have simultaneously measured thermopower S and electrical resistivity ρ at the temperature range between 2 K and 300 K and under pressures up to 3.5 GPa. In the pressure region of P 2.3 GPa, ρ increases with increasing temperature, and shows an anomaly in the form of a kink at the Neel temperature TN. S(T) also reveals a kink at TN. Both ρ(T) and S(T) indicate a small pressure dependence at the low pressure range. However, ρ(T) and S(T) curves in the low temperature region suddenly change their features at P ≍ 2.3 GPa, where the magnetic ordering disappears. ρ linearly decreases with decreasing temperature, and shows a sudden drop at the valence transition temperature Tv ≍ 30 K. S(T) reveals a drastic increase at Tv, changing its sign from negative to positive around 35 K, and takes maximum at T ≍ 7 K. The thermal hysteresis was clearly observed in both ρ(T) and S(T) curves around Tv.