Pressure-induced valence transition and heavy fermion state in Eu₂Ni₃Ge₅and EuRhSi₃

We succeeded in growing single crystals of Eu₂Ni₃Ge₅ and EuRhSi₃ by the In-flux method, and measured the electrical resistivity under pressures. Both compounds are Eu-divalent antiferromagnets with the Néel temperatures T_N = 18.6 and 47.7 K, respectively. With increasing pressure, the resistivity in Eu₂Ni₃Ge₅ indicates a clear kink at T_v = 220K under 8.0 GPa, for example, which corresponds to a valence transition. The valence of Eu ions deviates from divalence toward trivalence. Correspondingly, antiferromagnetic ordering disappears completely. The low-temperature resistivity is, surprisingly, very similar to the resistivity of a well-known heavy fermion superconductor CeCu₂Si₂, possessing a two-peak-structure based on the Kondo effect. In fact, the A value of the resistivity ρ = ρ₀ + AT² in the Fermi liquid relation becomes large, A = 0.3 μΩ·cm=K² at 8.0 GPa. The similar characteristic features are observed in another compound EuRhSi₃.