EXPERIMENTAL VERIFICATION AND CONTROL OF SPIN LIQUID STATE

本课题的目的是通过实验验证和控制理论预测在某些低维磁体中由于量子自旋抛射和自旋受挫效应可能存在的自旋液体复合物。为此，我们与许多其他研究小组合作，合成了各种模型量子系统，并应用了各种互补技术，包括先进的晶体制备、核磁共振、电子自旋共振、中子散射、介子自旋弛豫、高场磁化以及系统磁化率和比热测量。我们的研究总结如下。1)合成了S=1/2反铁磁链Cu (C_6H_7N)_2Br_2、S=1/2键交替链Cu (C_6H_7N)_2Cl_2、S=1/2自旋阶梯Cu_2(C_5H_<12 bbb_n_2)_2Cl_4、Cu_2(C_5H_<12 bbb_n_2) _2Bra_4等模型物质。2) S=1/2子元组成的复合自旋系统的量子效应研究。例如，我们对三聚链体系3CuCI_2-2dx进行了高达800GHz的高频ESR研究，该体系由三个S=1/2自旋组成的铁磁三聚体在一维上进行了反铁磁耦合。我们观察到复合自旋的特殊行为特征。具有非均匀空间结构的系统。3)量子自旋间隙相的控制。我们探索了在具有自旋间隙的量子单线态基态系统中，通过施加强磁场或掺杂杂质离子来诱导相变的可能性。例如，在S=2/3二聚体系Cs_3Cr_2Cl_3中，我们观察到在高达40T的三个受限场区连续相变。

The purpose of this project is to verify experimentally and control the possible spin liquid syate which is theoretically predicted to be exist in some low dimensional magnets, due to the quantum spin ejjects and spin frustration effects. For this purpose, we synthesized a various kind of model quantum systems and applied various complementary techniques, including advanced crystal preparation, nuclear Magnetic resonance, electron spin resonance, neutron scattering, muon spin relaxation, high field magnetization as well as sysceptobility and specific heat measurements, in cooperation with many other research groups. A summary of our research is as follows.1) Synthesis of the model substances such as S=1/2 antiferromagnetic chain Cu (C_6H_7N)_2Br_2, S=1/2 bond alternating chain Cu (C_6H_7N)_2Cl_2, S=1/2 spin ladder Cu_2(C_5H_<12>N_2)_2Cl_4, Cu_2 (C_5H_<12>N_2) _2Bra_4 and so on.2) Study of quantum effects of composite spin systems composed of S=1/2 subelements.For example, we performed high-frequency ESR study up to 800GHz of trimerized chain system 3CuCI_2-2dx, in which ferromagnetic trimers consisting of three S=1/2 spins coupled antiferromagnetically in one dimension. We observed peculiar behaviors characteristic of composite spin. system with nonuniform spatial structure.3) Control of quantum spin-gappped phase.We explored the possible induced-phase transition in the quantum singlet ground state systems with spin gap by applying high magnetic field or by doping impurity ions. For example, we observed successive phase transitions at three restricted field regions up to 40T in the S=2/3 dimerized system Cs_3Cr_2Cl_3.