Synthesis of the two-dimensional orthogonal dieter compound with an exact dieter ground state and investigation of its magnetic properties

本项目是关于Shastry-Sutherland模型的实验实现，这是我在大约5年前发现的二维正交系SrCu2(BO_3)2，其目的是阐明与其特殊拓扑结构有关的磁性，并利用一些化学和物理方法来诱导量子相变。结果发现，物理压力对调谐基态是非常有效的。即使在10kbar左右的压力作用下，自旋能隙也减小了一半，当进一步施加压力时，我们发现了相分离的趋势。这一结果与该化合物中较弱的自旋-单线态离某些其他态的相界很近的理论建议是一致的。与其他团队的合作也是成功的：使用我生长的优质晶体进行的高场核磁共振研究揭示了1/8平台状态下的磁性超结构，以及作为温度和磁场函数的奇异相变的性质，其结果发表在《科学》杂志上。这项研究促使理论家重新考虑他们的理论，因为现有的理论不能复制实验确定的上层建筑。我们还寻找了在拓扑上等价于Shastry-Suhherland模型的自旋化合物。发现Nd2BaZO5对应于该模型的另一个例子，但符合经典自旋。通过中子衍射实验确定了该材料的磁结构。本文研究了以SrCu2(BO_3)_2为晶格的新型磁阻体系。利用离子交换反应，我们新合成了低维磁性材料(CuCl)Ca_2Ta_3O_(10&gt)和(FeCl)Ca_2Ta_3O_(10&gt；10)，其中一些材料表现出有趣的磁性，可能源于磁性离子的低维网络。

The purpose of this project on the experimental realization of Shastry-Sutherland model, the two-dimensional orthogonal dieter system SrCu_2(BO_3)_2 that I discovered about 5 years ago, is to clarify the magnetic properties which are related to its special topology and to induce quantum phase transition, utilizing some chemical as well as physical method. As a result, physical pressure was found to be very effective for tuning the ground state. Even the application of pressure about 10kbar results in the reduction of spin gap which is as half as that without pressure, and when further pressure is applied, we have found a tendency of phase separation. This result is in consistent with the theoretical suggestion that the dieter spin-singlet state in this compound resides very close to the phase boundaries to some other states. The collaboration with other groups was also successful: the high-field NMR study using the good-quality crystal grown by me has revealed the magnetic superstructure at the 1/8 plateau state and nature of exotic phase transitions as a function of temperature and magnetic field, the result of which was published in Science. This study triggered theoreticians to reconsider their theory, since existing theories could not reproduce experimentally determined superstructure. We also search for the spin compound which is topologically equivalent to the Shastry-Suhherland model. Nd_2BaZnO_5 was found to correspond to another example of such model but with classical spins. We determined the magnetic structure of this material by neutron diffraction experiment. The search for the new magnetically frustrated systems based on the square lattice as in SrCu_2(BO_3)_2 has been conducted. By utilizing the ion-exchange reaction, we newly synthesized the low-dimensional magnetic materials such as (CuCl)Ca_2Ta_3O_<10> and (FeCl)Ca_2Ta_3O_<10>, some of which show interesting magnetic properties presumably arising from the low-dimensional network of magnetic ions.