EuCu₂Ge₂Quantum Criticality of Valence Transition of Antiferromagnetic Compound EuCu2Ge2

Abstract

We have investigated the effect of pressure on the electronic state of antiferromagnetic compound EuCu₂Ge₂ by electrical resistivity measurement up to 10 GPa using a cubic anvil cell apparatus. On applying pressure, the Néel temperature of 𝑇_N=15 K at ambient pressure increases monotonically and reaches a maximum value 27 K at 6.2 GPa.

Thereafter, however, 𝑇_N suddenly drops to zero at 6.5 GPa, suggesting the quantum critical point driven by the valence transition of Eu from a nearly divalent (Eu²⁺) to a nonmagnetic trivalent (Eu³⁺) state. Here we would like to mention that this result is the first observation of a valence transition among the Eu-based compounds.