Electronic States in EuCu2(Ge1-xSix)2 Based on the Doniach Phase Diagram

We succeeded in growing single crystals of EuCu2(Ge1-xSix)(2) (x = 0-1) by the Bridgman method using a Mo crucible and measured the electirical resistivity, specific heat, magnetic susceptibility, and magnetization, together with the electrical resistivity under pressure. EuCu2(Ge-1_Si-x(x))(2) compounds follow the Doniach phase diagram as a function of the x content. Namely, EuCu2(Ge-1_Si-x(x))(2) compounds exhibit antiferromagnetic ordering at a Neel temperature of T-N = 15 K in EuCu2Ge2 (x = 0), a maximum of T-N similar or equal to 20 K at x similar or equal to 0.5, T-N -> 0 at x similar or equal to 0.7, and a moderate heavy-fermion state at x = 0.8 and 1 (EuCu2Si2). The present result is reasonably consistent with the previous studies carried out using arc-melted polycrystal samples. A similar change in the electronic states was also found to be realized under pressure P for x = 0, 0.45 and 0.6. The Neel temperature of T-N = 15 K for x = 0 (EuCu2Ge2) increases slightly as a function of pressure, at a rate of dT(N)/dP = 3.0 K/GPa, reaches a maximum of T-N = 27 K at around 5-6 GPa, decreases steeply, and becomes zero at a critical pressure of P-c similar or equal to 7 GPa. A moderate heavy-fermion state is realized at 8 GPa. Similar results were also obtained for x = 0.45 and 0.6, with smaller critical pressures of P-c similar or equal to 4.5 and 2 GPa, respectively.