Investigation for the pressure-induced anomalous magnetism of the low dimensional organic quantum spin systems

在低维量子自旋材料和有机磁体领域，由于量子效应的显著存在，存在单重基态的自旋隙系统受到了广泛的关注。我们精确地测量了一个有机低维量子自旋系统在压力下的磁化率和磁化率，发现了其反常的磁性行为。典型的自旋-佩尔斯物质MEM-[TCNQ]_2在低温下的磁化率随温度的降低而增大，其磁化率可以用奎尔定律来描述。为了澄清这种压力下的异常磁行为，我们进行了两年的研究。本文研究了三种自旋间隙体系，即(1)Haldane物质Ni(C_5H_<14 bbb_nq_2)_2N_3PF_6,(2)量子阶梯物质Cu_2(C_6H_<12>N_2)_2Cl_4及其相关物质，(3)自旋- peierls物质MEM-[TCNQ]_2及其相关物质。制成了良好的单晶，并精确地测量了它们的磁性能作为压力的函数。通过对单晶在单轴压力下的测量，我们发现MEM-[TCNQ]_2的磁性能表现出明显的各向异性。为了阐明MEM-[TCNQ]_2在压力下磁化率增加的原因，我们在常规x波段ESR仪器上使用手工制作的压力池测量了单轴压力下的电子自旋共振（ESR）谱。ESR谱的温度依赖关系表明，在压力下存在两种不同的自旋，这是由磁化率和磁化率等宏观测量所假设的。

Spin-gap systems where singlet-ground states are observed because of significant quantum effect have attracted attention in the field of low-dimensional quantum spin materials and organic magnets. We have precisely measured the magnetization and magnetic susceptibility for an organic low-dimensional quantum spin system under pressure and found the anomalous magnetic behavior. The magnetic susceptibility of a typical spin-Peierls substance, MEM-[TCNQ]_2, under pressure increases with decreasing temperature at low temperatures and it is roughly described by Cuire's law.We have studied to clarify such anomalous magnetic behavior under pressure for two years. Three kinds of spin-gap systems, (1)Haldane substance Ni(C_5H_<14>NQ_2)_2N_3PF_6, (2)quantum ladder substances : Cu_2(C_6H_<12>N_2)_2Cl_4 and related substances, (3)spin-Peierls substances : MEM-[TCNQ]_2 and a related substance, were treated in this study. Good single crystals were made and their magnetic properties were measured precisely as a function of pressure. As a result of the measurement for a single crystal under uniaxial pressure, we found that the magnetic properties of MEM-[TCNQ]_2 show significant anisotropy. In order to clarify the origin of the increase of the magnetic susceptibility under pressure for MEM-[TCNQ]_2, we have measured the electron-spin-resonance (ESR) spectra under uniaxial pressure by using a hand-made pressure cell for a conventional X-band ESR instrument : The temperature dependence of the ESR spectra show that there are two different spins under pressure, which has been supposed by the macroscopic measurement such as the magnetization and magnetic susceptibility.