Magnetic properties and negative colossal magnetoresistance of the rare earth Zintl phase EuIn₂As₂

Large, high quality single crystals of a new Zintl phase, EuIn ₂As₂, have been synthesized from a reactive indium flux. EuIn₂As₂ is isostructural to the recently reported phase EuIn₂P₂, and it is only the second reported member of the group of compounds with formula AM₂X₂ (A = alkali, alkaline earth, or rare earth cation; M = transition or post-transition metal; and X = Group 14 or 15 element) that crystallizes in the hexagonal space group P6₃/mmc (a = 4.2067(3) Å, c = 17.889(2) Å and Z = 2). The structure type contains layers of A²⁺ cations separated by [M ₂X₂]^2- layers along the crystallographic c-axis. Crystals of the title compound were mounted for magnetic measurements, with the crystallographic c-axis oriented either parallel or perpendicular to the direction of the applied field. The collective magnetization versus temperature and field data indicate two magnetic exchange interactions near 16 K, one involving Eu²⁺⋯Eu²⁺ intralayer coupling and the other involving Eu²⁺⋯Eu²⁺ coupling between layers. EuIn₂As₂ is metallic and magnetoresistive, as is the isostructural phosphide, and both compounds have coincident resistivity and magnetic ordering transitions, consistent with the observation of colossal magnetoresistance. Negative colossal magnetoresistance (MR = {[p(H) - p(0)]/ρ(H)} x 100%) of up to -143% (at T = 17.5 K, H = 5 T) is observed for EuIn₂As₂, approximately half of that observed for the more resistive phosphide, which has a higher magnetic ordering temperature and local moment coupling strength.