Studies on Quantum Magnets by Alternating and Ladderlike Chains

我们研究了一些被视为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=1/2两腿自旋梯和S=1/2锯齿链的镍和铜配合物。我们对S=1键交替链进行了磁化率和磁化强度测量，并比较了实验结果与计算出来的。然后，评估键交替比和交换常数。这项研究的一些显着发现包括观察到对应于磁化量子化的 1/2 磁化平台，以及通过观察某种镍键交替链化合物中的无间隙行为来实验验证 Affleck-Haldane 猜想。此外，我们还得到了S=1键交替链中单线态二聚体基态的证据。第二个和第三个化合物与量子亚铁磁体的研究有关。每种化合物中磁化率乘以温度的温度依赖性是亚铁磁链的典型特征。在S=1/2 F-F-AF-AF链化合物中，我们观察到饱和场附近磁化强度急剧增加，并从极短相关长度的角度对其进行了讨论。对于S=1/2两腿梯化合物，我们进行了磁化率和比热测量，并将结果与​​计算结果进行了比较。在有间隙相中，实验和计算之间的一致性非常好，而在可能由 Tomonaga-Luttinger 液体描述的无间隙相中，一致性变差。我们根据最近的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.