Electronic and magnetic properties of EuNi_2-δSb₂structural variants

X-ray diffraction, magnetic susceptibility, magnetization, heat capacity and electrical resistivity results are reported for single crystals of two structural variants of EuNi_2-δSb₂that crystallize in the CaBe₂Ge₂and ThCr₂Si₂-type structures. While the former occurs with a stoichiometric ratio, the latter exhibits a Ni site vacancy (δ= 0.36). Both systems exhibit similar magnetic behavior at elevated temperatures, where there is an isotropic Curie-Weiss temperature dependence that indicates an antiferromagnetic exchange interaction between divalent europium ions, although it is stronger for the CaBe₂Ge₂-variant. At low temperatures, the differing structural environments that surround the Eu ions result in distinct ordering behavior. The CaBe₂Ge₂-variant orders antiferromagnetically nearT_N1= 6.9 K and then undergoes a first order phase transition atT_M= 4.6 K. The ThCr₂Si₂-variant exhibits simpler behavior, with antiferromagnetic ordering atT_N2= 5.6 K. For both compounds, an applied magnetic field suppresses the ordering temperatures and induce metamagnetic phase transitions, while applied pressure causes the ordering temperatures to increase. From these results, EuNi_2-δSb₂emerges as a useful system in which to study the impact of structural variation on magnetism in a Eu-based metal.