Negative magnetoresistance in a magnetic semiconducting zintl phase: Eu₃In₂P₄

A new rare earth metal Zintl phase, Eu₃In₂P ₄, was synthesized by utilizing a metal flux method. The compound crystallizes in the orthorhombic space group Pnnm with the cell parameters a = 16.097(3) Å, b = 6.6992(13) Å, c = 4.2712(9) Å, and Z = 2 (T = 90(2) K, R1 = 0.0159, wR2 = 0.0418 for all data). It is isostructural to Sr₃In₂P₄. The structure consists of tetrahedral dimers, [In₂P₂P_4/2]^6-, that form a one-dimensional chain along the c axis. Three europium atoms interact via a Eu-Eu distance of 3.7401(6) Å to form a straight line triplet. Single-crystal magnetic measurements show anisotropy at 30 K and a magnetic transition at 14.5 K. High-temperature data give a positive Weiss constant, which suggests ferromagnetism, while the shape of susceptibility curves (χ vs T) suggests antiferromagnetism. Heat capacity shows a magnetic transition at 14.5 K that is suppressed with field. This compound is a semiconductor according to the temperature-dependent resistivity measurements with a room-temperature resistivity of 0.005(1) Ω m and E_g = 0.452(4) eV. It shows negative magnetoresistance below the magnetic ordering temperature. The maximum magnetoresistance (Δρ/ρ(H)) is 30% at 2 K with H = 5 T.