Studies on Quantum Magnets by Alternating and Ladderlike Chains

我们研究了一些镍铜配合物，它们被认为是S=1反铁磁键交替链、S-1/2和1自旋交替链、S=1/2铁磁-铁磁-反铁磁-反铁磁（F-F-AF-AF）链、S=1/2两腿自旋阶梯链和S=1/2之形链。我们对S=1键交替链进行了磁化率和磁化率测量，并将实验结果与计算结果进行了比较。然后计算了键的交变比和交换常数。本研究中值得注意的发现是观测到对应磁化量子化的1/2磁化平台，并通过观察某镍键交链化合物的无间隙行为实验验证了Affleck-Haldane猜想。此外，我们还得到了S=1键交替链中单重二聚体基态存在的证据。第二个和第三个化合物与量子铁磁体的研究有关。每种化合物的磁化率与温度的温度依赖关系是典型的铁磁链。在S=1/2 F-F-AF-AF链化合物中，我们观察到饱和场周围磁化强度的急剧增加，并以极短的相关长度进行了讨论。对于S=1/2两腿梯化合物，我们进行了敏感性和比热测量，并与计算结果进行了比较。在间隙相中，实验与计算的一致性很好，而在可能由Tomonaga-Luttinger液体描述的无间隙相中，一致性变得很差。我们根据最近的一个理论和核磁共振实验讨论了这种偏差。

We investigated some nickel and copper complexes which are regarded as the S=1 antiferromagnetic bond alternating chains, the S-1/2 and 1 spin alternating chain, the S=1/2 ferromagnetic-ferromagnetic-antiferromagnetic-antiferromagnetic (F-F-AF-AF) chain, the S=1/2 two-leg spin ladder and the S=1/2 zigzag chain.We performed susceptibility and magnetization measurements on the S=1 bond alternating chains and compared the experimental results with the calculated ones. Then, the bond alternating ratios and the exchange constants are evaluated. Some of the remarkable findings in this study are the observation of the 1/2 magnetization plateau which corresponds to the quantization of magnetization and the experimental verification of the Affleck-Haldane conjecture by the observation of the gapless behavior in a certain nickel bond alternating chain compound. Moreover, we got evidence for the singlet-dimer ground state in an S=1 bond alternating chain.The second and the third compounds are related to the studies on quantum ferrimagnets. The temperature dependence of magnetic susceptibility times temperature in each compound is typical of the ferrimagnetic chain. In the S=1/2 F-F-AF-AF chain compound, we observed a steep increase of magnetization around the saturation field and discussed it in terms of the extremely short correlation length.For the S=1/2 two-leg ladder compound, we performed susceptibility and specific heat measurements and compared the results with the calculated ones. In the gapped phase, the agreement between the experiment and the calculation is excellent, while the agreement becomes poor in the gapless phase that is probably described by the Tomonaga-Luttinger liquid. We discussed this deviation in terms of a recent theory and a NMR experiment.