狄拉克材料CaMnBi_2的单晶制备与物理性质研究

Single Crystal Growth and Physical Properties of Dirac Material CaMnBi_2

采用高温助溶剂方法制备出各向异性狄拉克材料Ca Mn Bi2的高质量大尺寸单晶样品。综合运用X射线衍射(XRD)、扫描电镜-能量色散X射线光谱仪系统(SEM-EDX)、综合物性测量系统(PPMS)等测试手段对Ca Mn Bi2高质量单晶样品的晶体结构、化学成分、电学、磁学和热学性质进行了系统的研究。结果表明:Ca Mn Bi2的晶体结构是由Mn Bi(1)四面体层、Ca原子层以及Bi(2)四方格子层构成,它们按照Mn Bi(1)-Ca-Bi(2)-Ca-Mn Bi(1)的顺序沿c轴方向堆垛形成"三明治"型层状结构;这些不同的结构层对物理性质有不同的作用,其中Bi(2)四方格子层对电输运性质和狄拉克电子起主要作用,而Mn Bi(1)层中Mn2+对磁学性质的起着决定作用。这两个功能层的共同作用下该材料具有层状准二维电子系统的典型特征,并且表现出金属反铁磁(TN=270 K)行为。

High quality and large size single crystal sample of anisotropic Dirac material Ca Mn Bi2 was synthesized by high temperature flux method. The crystal structure,chemical composition,electrical,magnetic and heat properties were systematic studied by the measurements of the X-ray diffraction（ XRD） of single crystal and powder,scanning electron microscope-energy dispersive X-ray spectroscopy system（ SEM-EDX）,physical property measurement system（ PPMS） of Quantum Design with the vibrating sample magenetometer（ VSM） option. The results show that crystal structure of Ca Mn Bi2 is a sandwich layer structure in which there are three layers： Mn Bi（ 1） tetrahedra layer,Ca atoms layer and Bi（ 2） square nets layer,and these layers are arranged by the alignment of Mn Bi（ 1）-Ca-Bi（ 2）-Ca-Mn Bi（ 1） along c axis. These layers play different roles in physical properties. For instance,the Bi（ 2） square nets layer plays important roles in electrical transport property and dirac electrons,but Mn Bi（ 1）tetrahedra layer plays important roles in magnetic property. This material has the typical features of layered quasi 2D electron system and shows an antiferromagnetic（ TN= 270 K） metal behavior by the combined effects of these function layers.