Crystal Structure and a Giant Magnetoresistance Effect in the New Zintl Compound Eu₃Ga₂P₄

Single-crystalline samples of a new Zintl compound, Eu₃Ga₂P₄, have been synthesized by a Ga-flux method. Eu₃Ga₂P₄ is found to crystallize in a monoclinic unit cell, space group C2/c, isostructural to Ca₃Al₂As₄. The structure is composed of a pair of edge-shared GaP₄ tetrahedra, which link by corner-sharing to form Ga₂P₄ two-dimensional layers, separated by Eu²⁺ ions. Magnetic susceptibility showed a Curie–Weiss behavior with an effective magnetic moment consistent with the value for Eu²⁺ magnetic ions. Below 15 K, ferromagnetic ordering was observed and the saturation magnetic moment was 6.6 μ_B. Electrical resistivity measurements on a single crystal showed semiconducting behavior. Resistivity in the temperature range between 280 and 300 K was fit by an activation model with an energy gap of 0.552(2) eV. The temperature dependence of the resistivity is better described by the variable-range-hopping model for a three-dimensional conductivity, suggesting that Eu–P bonds are involved in the conductivity. A large magnetoresistance, up to −30%, is observed with a magnetic field H = 2 T at T = 100 K, suggesting strong coupling of carriers with the Eu²⁺ magnetic moment.