We have synthesized polycrystalline samples of Eu2Pt6(Al1−xGax)15 (x = 0, 0.05, 0.1, 0.2, 0.3, and 1) and examined electrical resistivity, magnetic susceptibility, high-field magnetization, and X-ray absorption spectra at the Eu L3-edge. With increasing x up to 0.1, the first-order valence transition is shifted to low temperatures. For x ≥ 0.1, a nearly divalent state is stabilized down to the lowest temperature, and an antiferromagnetic order emerges below TN = 13–16 K. For x = 0 and 0.05, magnetization curves in pulsed magnetic fields at T = 4.2 K clarify a field-induced valence transition at Bv = 29 and 19 T, respectively. The ratio of Bv to the valence transition temperature Tv is close to a universal value of other Eu-based systems with a different crystal structure (ThCr2Si2 type). The phase boundary curve in the T–B phase diagram is discussed thermodynamically.
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