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 electrical resistivity, specific heat, magnetic susceptibility, and magnetization, together with the electrical resistivity under pressure. EuCu2(Ge1−xSix)2 compounds follow the Doniach phase diagram as a function of the x content. Namely, EuCu2(Ge1−xSix)2 compounds exhibit antiferromagnetic ordering at a Néel temperature of TN = 15 K in EuCu2Ge2 (x = 0), a maximum of TN ’ 20 K at x’ 0.5, TN → 0 at x’ 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 Néel temperature of TN = 15 K for x = 0 (EuCu2Ge2) increases slightly as a function of pressure, at a rate of dTN=dP = 3.0 K=GPa, reaches a maximum of TN = 27 K at around 5–6 GPa, decreases steeply, and becomes zero at a critical pressure of Pc ’ 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 Pc ’ 4.5 and 2 GPa, respectively.
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