Unique Structure Type and Antiferromagnetic Ordering in Semiconducting Eu2InSnP3

Rare-earth-containing ternary pnictides formed with main group elements occupy a chemical space where they can span insulating to metallic behavior, and they often exhibit low-dimensional structures where magnetic ordering can be tuned by moderate fields. Investigating compounds between semimetallic EuIn₂P₂ and EuSn₂P₂ led to the formation of an ordered quaternary phase Eu₂InSnP₃, which forms in the orthorhombic space group Pnma. The Eu²⁺ ions in Eu₂InSnP₃ form a hollandite-like channeled matrix of edge-sharing EuP₆ octahedra. These Eu²⁺ donate electrons to a [InSnP₃]^4– polyanion which exhibits a distinct In–Sn bond to maintain charge balance in the Zintl framework. This bonding requirement and our experimental synthesis attempts with varying stoichiometries indicate that the In and Sn are fully ordered, leading to semiconducting behavior. First-principles simulations find the smallest band gap to be indirect of about 0.5 eV, but close in energy to a direct gap. The magnetic behavior of Eu₂InSnP₃ shows a low-field antiferromagnetic ordering at T_N = 12 K and a spin-flop transition around 0.8 T at 2 K. The progression of magnetic states is complex, but can be ascertained by considering the connectivity of the two inequivalent magnetic sites in the compound and the low anisotropy of the 4f⁷ Eu²⁺ ion. In all, the ability of covalent In–Sn bonding to open a semiconducting gap is evidence of the delicate interactions in these compounds and their propensity to exhibit uncommon structural motifs.