New Development of the Quadrupole Interaction studied by Thulium Hexaboride (TmB_6)

这一研究项目的目的是阐明最近许多研究人员感兴趣的四极相互作用的本质。在这一研究领域感兴趣的材料之一是我们多年来一直在研究的CeB6。CeB_6只有一个4f电子，这是四足相互作用的起源。另一方面，Tm有13-4f电子，TmB_6相当于CeB_6，因为Tm的4f壳层充满了14个电子。因此，TMB_6的四极特性是非常重要的研究课题。而TMB_6在常温常压下不存在物相。我们找到了一个方法来打破这个问题的瓶颈。在CeB_6中，La取代Ce不改变近藤型单重离子的性质。相反，在Ce_xLa_t；1-x&gt；B_6的研究中出现了许多新的信息。用浮区法成功地生长出了高质量的Tm_xLa_(1-x)Gt；B_6，Tm_xYb_(？)它们的电阻率和磁化强度测量表明，Tm_xYb_&lt；1-x&gt；B_6在7.5K和Tm_xLa_&lt；1-x&gt；B_6在4.5K发生相变。很难考虑这些相变时的磁序，因为Tm只包含25%。相变被认为是由四极相互作用引起的。因此，现在需要许多其他测量比热、中子散射等的方法。

The purpose of this research project is to elucidate the essential nature of quadrupole interactions in which many researchers are interested in recently. One of the interested materials in this research area is CeB_6 that is investigated by us for long years. CeB_6 has only one 4f electron that is the origin of the quadrupode interactions. On the other hand, Tm has 13-4f electrons, then TmB_6 is counterpart to CeB_6 because 4f shell is full for 14 electrons. Therefore, the quadrupole nature of TmB_6 is very important research subject. However, TmB_6 is not found its phase in room temperature and in normal pressure. We found a method to break the bottleneck of this problem. In CeB_6, the Kondo-type singlet-ion nature is not changed by substitution of Ce by La. On the contrary, many new informations appeared in the investigations of Ce_xLa_<1-x>B_6 by the substitution. We succeeded to grow good quality of single crystals of Tm_xLa_<1-x>B_6, Tm_xYb_<1-x>B_6 by floating zone method. They shows phase transition at 7.5 K for Tm_xYb_<1-x>B_6 and at 4.5 K for Tm_xLa_<1-x>B_6 by the electrical resistivity and the magnetization measurements. It is hard to consider the magnetic order at these phase transitions because Tm is contained by only 25%. The phase transitions are thought to be attributed to quadrupole interactions. Therefore, many other measurements of specific heat, neutron scattering, etc. are needed now.