Negative Magnetoresistance in a Magnetic Semiconducting Zintl Phase: Eu₃In₂P₄

A new rare earth metal Zintl phase, Eu3In2P4, 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, [In2P2P4/2]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 Eg = 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.本研究采用金属助熔剂法（metal flux method）成功合成了一种新型稀土金属齐特林相（Zintl phase）Eu3In2P4。该化合物结晶于正交晶系空间群Pnnm，晶胞参数为a=16.097(3) Å、b=6.6992(13) Å、c=4.2712(9) Å，晶胞化学式单元数Z=2（测试温度T=90(2) K，全数据精修的R1因子为0.0159，加权R2因子为0.0418）。该化合物与Sr3In2P4同构。其结构由四面体二聚体[In2P2P4/2]6-构成，该二聚体沿c轴形成一维链。三个铕原子通过3.7401(6) Å的Eu-Eu间距相互作用，形成直线型三原子簇。单晶磁性测试结果显示，该化合物在30 K时表现出磁各向异性，并在14.5 K处出现磁相变。高温测试得到的外斯常数为正值，提示体系存在铁磁性相互作用，但磁化率曲线（χ vs T）的形状却表明其呈现反铁磁性。热容测试表明，该化合物在14.5 K处存在磁相变，且该相变可被外磁场抑制。根据变温电阻率测试结果，该化合物属于半导体，其室温电阻率为0.005(1) Ω·m，禁带宽度Eg=0.452(4) eV。该化合物在磁有序温度以下表现出负磁电阻效应，在2 K、外磁场H=5 T时，最大磁电阻相对变化率（Δρ/ρ(H)）可达30%。