Sigmoidal Decrease of the Curie Temperature in the Solid Solutions Eu1-xCaxPtIn2

The MgCuAl2-type intermetallic phases CaPtIn2 and EuPtIn2 form a complete set of solid solutions Eu1-xCa x PtIn2 with a Vegard-type, almost linear decrease of the cell volume with increasing calcium content. The structure of Eu0.579(16)Ca0.421PtIn2 was refined from single-crystal X-ray diffractometer data: Amm2, a = 783.09(2), b = 442.91(6), c = 1,055.54(4) pm, wR = 0.0356, 1054 F2 values and 33 variables. This subgroup refinement yielded a europium accumulation on site 2a and a calcium accumulation on site 2b, pointing to an ordered arrangement. Temperature dependent magnetic susceptibility studies showed Curie-Weiss paramagnetism for all Eu1-xCa x PtIn2 samples. Ferromagnetic ordering is detected at low temperature with a decrease of the Curie temperature from 32.8(1) K for EuPtIn2 to 2.0(1) K for Eu0.1Ca0.9PtIn2. The decrease in TC proceeds in a sigmoidal manner with the inflection point close to the ordered composition Eu0.5Ca0.5PtIn2. The stable divalent europium ground states are corroborated by 151Eu M & ouml;ssbauer spectroscopy.