Magnetic Properties and Negative Colossal Magnetoresistance of the Rare Earth Zintl phase EuIn2AS2

Large, high quality single crystals of a new Zintl phase, EuIn(2)AS(2), have been synthesized from a reactive indium flux. EuIn(2)AS(2) is isostructural to the recently reported phase EuIn2P2, and it is only the second reported member of the group of compounds with formula AM(2)X(2) (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 P6(3)/mmc (a = 4.2067(3) angstrom, c = 17.889(2) angstrom and Z = 2). The structure type contains layers of A(2+) cations separated by [M2X2](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+center dot center dot center dot Eu2+ intralayer coupling and the other involving Eu2+center dot center dot center dot Eu2+ coupling between layers. EuIn(2)AS(2) is metallic and magneto resistive, as is the isostructural phosphide, and both compounds have coincident resistivity and magnetic ordering transitions, consistent with the observation of colossal magneto resistance. Negative colossal magneto resistance (MR = {[rho(H) - rho(0)]/rho(H) x 100%) of up to -143% (at T = 17.5 K, H = 5 T) is observed for EuIn(2)AS(2), approximately half of that observed for the more resistive phosphide, which has a higher magnetic ordering temperature and local moment coupling strength.