Experimental Study of New Universality Classes in Magnetic Phase Transition

用核磁共振、电子自旋共振、中子散射、磁化率和高场磁化强度等方法对各种模型物质进行了实验研究。1.在1.4K到300K之间的精确测量中，我们发现了堆叠的三角形晶格反铁磁体ABX3和AMO2在1.4K到300K之间发生了丰富的磁相变包括一种新的与手征简并有关的普适性相变。磁场与温度的相图根据它们的磁反对称性被分为两类。2.量子自旋系统研究了一维Heisenberg系统由于量子自旋效应而产生的非磁性基态。我们观察到非磁性杂质对Haldane系统、Spin-Peierls系统和交替线性链系统的显著不同的影响，并讨论了结果的物理意义。

The purpose of the present research is to elucidate the phase transitions in low dimensional magnetic system, such as frustrated triangular lattice antiferromagnet and quantum spin one-dimensional antiferromagnet.We performed the experimental study on various model substances using nuclear magnetic resonance (NMR), electron spin resonance (ESR), neutron scattering, susceptibity and high field magnetization maeasuments.1.Triangular lattice antiferromagnetOur precise measurements between 1.4K and 300K under static magnetic fields up to 40 T,occasionally up to 110 T,revealed a rich variety of magnetic phase transitions in the stacked triangular lattice antiferromagnets ABX3 and AMO2, including a novel phase transition which belongs to a new universality class linked to chiral degeneracy.The magnetic field versus temoerature phase diagrams are classified into two types depending on their magnetic antisotropies.2.Quantum spin systemNonmagnetic groud states due to quantum spin effect were studied for one-dimensional Heisenberg systems.We observed remarkable differneces in the nonmagnetic impurity efect on the Haldane system, spin-Peierls system and alternating linear chain system and disscussed the physical sihnificance of the results.