Electronic and Magnetic Properties of EuNi_2-xSb₂ Structural Variants

XRD, magnetic susceptibility, magnetization, heat capacity, and resistivity results are reported for single crystals of two structural variants of EuNi_2-xSb₂. While the CaBe₂Ge₂-type structure forms with a stoichiometric ratio, the ThCr₂Si₂-type structure exhibits a Ni site vacancy of 18%. Both systems show Curie-Weiss temperature dependence at elevated temperatures, indicating an antiferromagnetic exchange interaction between the Eu²⁺ ions. At low temperatures, the different structural environments give rise to distinct ordering behavior. The CaBe₂Ge₂-variant first orders antiferromagnetically near T_N2=6.9K and then undergoes a first order transition at T₃=4.6K. The ThCr₂Si₂-variant orders antiferromagnetically at T_N1=5.6K. The 4f entropy recovered by the antiferromagnetic ordering is consistent with the predicted J=7/2 Hund's rule multiplet values for the ThCr₂Si₂-variant, while it is reduced for the CaBe₂Ge₂-variant. Thus, EuNi_2-xSb₂ emerges as a useful system in which to study the impact of structural variation on electronic correlations.