Crystal structure and a giant magnetoresistance effect in the new zintl compound Eu ₃Ga ₂P ₄

Single-crystalline samples of a new Zintl compound, Eu ₃Ga ₂P ₄, have been synthesized by a Ga-flux method. Eu ₃Ga ₂P ₄ is found to crystallize in a monoclinic unit cell, space group C2/c, isostructural to Ca ₃Al ₂As ₄. The structure is composed of a pair of edge-shared GaP ₄ tetrahedra, which link by corner-sharing to form Ga ₂P ₄ two-dimensional layers, separated by Eu ²⁺ ions. Magnetic susceptibility showed a Curie-Weiss behavior with an effective magnetic moment consistent with the value for Eu ²⁺ 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 Eu ²⁺ magnetic moment.