Magnetic Properties and Negative Colossal Magnetoresistance of the Rare Earth Zintl phase EuIn₂As₂

Abstract

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 EuIn(2)P(2), 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) A, c = 17.889(2) A and Z = 2). The structure type contains layers of A(2+) cations separated by [M(2)X(2)](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 Eu(2+)...Eu(2+) intralayer coupling and the other involving Eu(2+)...Eu(2+) coupling between layers. EuIn(2)As(2) 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 = {[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.

Magnetism and Negative Magnetoresistance of Two Magnetically Ordering, Rare-Earth-Containing Zintl phases with a New Structure Type: EuGa2Pn2 (Pn = P, As)

“…18,22,[26][27][28][29] AM 2 X 2 phases can theoretically achieve a remarkable structural diversity, depending on factors such as the relative sizes and coordination preferences of the large number of elements that can be accommodated, and by taking advantage of the variable connectivity possible for main group polyanions. Thus, our group has recently reported the synthesis and structural characterization of hexagonal EuIn 2 Pn 2 compounds (Pn = P, As; P6 3 /mmc), 8,14 which display structural similarities to the three common AM 2 X 2 structure types. The ThCr 2 Si 2 , CaBe 2 Ge 2 , CaAl 2-Si 2 , and EuIn 2 Pn 2 structure types all consist of [M 2 X 2 ] nanionic layers, which alternate with cation layers along one crystallographic direction.…”

“…The structures further differ in the number of crystallographically distinct europium atoms, which reside between the anion layers in both structures, with only one Eu site in the indium compounds as opposed to three in the lower symmetry gallium analogues. 8,14 A view of the structure of EuGa 2 Pn 2 is shown in Figure 1. Tables 2 and 3 provide positional parameters and selected distances and angles.…”

“…Magnetoresistance (MR) has been observed in several rare-earth Zintl analogues. 6,[8][9][10][14][15][16][17] It is thought that the MR behavior of rare-earth-containing Zintl phases originates from interactions between the localized magnetic moment on the rare-earth cations and the delocalized conduction electrons of the Zintl polyanions. Such materials could be useful in magnetic storage applications.…”

“…Many of these interesting properties are found in materials of composition AM 2 X 2 (M = transition or main group element, X=Group 13-15 element), which is a particularly diverse structural class. 8,14,[18][19][20][21][22] Recent discovery of colossal magnetoresistance (CMR) in several of the magnetically ordering AM 2 X 2 compounds (e.g., EuIn 2 P 2 and EuIn 2 As 2 ), 8,14 provides incentive for additional research into these types of compounds in order to provide correlations between material composition, structure, and the observed electrical, magnetic, and/or magneto-electronic properties.…”

Role of the dimensionality of the [GaX]2 network in the Zintl phases EuGa2X2

“…[4][5][6][7][8] EuIn 2 P 2 shows a metallic behavior at room temperature. 5 Below about 60 K, it turns into a semiconductor with a very narrow energy gap, which collapses in a magnetic field of a few tesla.…”