Sigmoidal decrease of the Curie temperature in the solid solutions Eu 1– x Ca x PtIn ₂

The MgCuAl 2 -type intermetallic phases CaPtIn 2 and EuPtIn 2 form a complete set of solid solutions Eu 1– x Ca x PtIn 2 with a Vegard-type, almost linear decrease of the cell volume with increasing calcium content. The structure of Eu 0.579(16) Ca 0.421 PtIn 2 was refined from single-crystal X-ray diffractometer data: Amm 2, a = 783.09(2), b = 442.91(6), c = 1,055.54(4) pm, w R = 0.0356, 1054 F 2 values and 33 variables. This subgroup refinement yielded a europium accumulation on site 2 a and a calcium accumulation on site 2 b , pointing to an ordered arrangement. Temperature dependent magnetic susceptibility studies showed Curie-Weiss paramagnetism for all Eu 1– x Ca x PtIn 2 samples. Ferromagnetic ordering is detected at low temperature with a decrease of the Curie temperature from 32.8(1) K for EuPtIn 2 to 2.0(1) K for Eu 0.1 Ca 0.9 PtIn 2 . The decrease in T C proceeds in a sigmoidal manner with the inflection point close to the ordered composition Eu 0.5 Ca 0.5 PtIn 2 . The stable divalent europium ground states are corroborated by 151 Eu Mössbauer spectroscopy.