Complex magnetic ordering in Eu₃InP₃: A new rare earth metal zintl compound

Eu₃InP₃ has been prepared as large single crystals with an indium flux reaction. The structure of the new compound is isotypic to Sr₃InP₃ and crystallizes in the orthorhombic space group Pnma with unit cell dimensions of a = 12.6517(15) Å, b = 4.2683(5) Å, and c = 13.5643(14) Å (Z = 4, T = 140 K, R1 = 0.0404, wR2 = 0.0971 for all data). The structure consists of one-dimensional chains of corner-shared distorted [InP₂P_2/2]^6- tetrahedra separated by rows of Eu²⁺ ions. Two of the three crystallographically distinct europium sites have a short Eu(1)-Eu(2) distance of 3.5954(7) Å, which yields Eu-Eu dimers. The Eu-P bond distances range from 2.974(2) to 3.166(2) Å. The temperature dependence of the conductivity indicates that Eu₃InP₃ is a small band gap semiconductor. Both magnetization and Eu-151 Mössbauer spectral measurements indicate that the europium in Eu₃InP₃ is divalent and that at least two magnetic transitions occur. Magnetization studies reveal magnetic transitions at 14, 10.4, and ∼5 K. These transitions are also observed in heat capacity studies of Eu₃InP₃. The Mössbauer spectra indicate that the two europium sites are ordered at 12 K and that all three europium sites are ordered at 8 K.