Study of Quantum Phenomena in a One-Dimensional Magnetic System

本课题的目的是阐明一维磁系统中的量子现象。主要研究结果如下：(1)对掺杂少量Cu的典型自旋单线链Heisenberg反铁磁体NENP进行了电子自旋共振（ESR）测量。在ESR光谱中得到了两组超精细结构。考虑到Cu核和电子自旋之间的超精细相互作用，以及在Cu原子附近的Ni位点诱导的分数自旋自由度，可以很好地解释这一结果。(2)在含3.3 at的NENP单晶上进行了稳定场高达8T和脉冲场高达40T的磁化测量。%铜。磁化强度在低场强下迅速增大，在4T以上达到饱和。当磁场进一步增大时，磁化强度又开始增大。基于3个S=1/2自旋模型，定量解释了低场区磁化强度的场依赖性。(3)在脉冲强磁场下对S=1一维海森堡反铁磁体TMNIN和NINAZ进行了磁化测量。在低场区，磁化强度很小，在临界场以上，磁化强度急剧增加。这种磁化行为与Katsumata等人之前在NENP中观察到的相似。由此，实验证实了TMNIN和NINAZ中Haldane间隙的存在。(4)通过对快速生长的NENP单晶的ESR和磁化测量，我们观察到了分数自旋自由度。

It is the aim of the present project to clarify the quantum phenomena in a one-dimensional magnetic system. The important findings obtained from this study are summarized below:(1)An electron spin resonance(ESR) measurement has been performed on a typical spin(S) one linear chain Heisenberg antiferromagnet NENP doped with a small amount of Cu. Two sets of hyperfine structure are obtained in the ESR spectrum. The result is well explained by taking into account the hyperfine interaction between the Cu nuclear and electron spins which couples with the fractional spin degrees of freedom induced at the Ni site neighboring the Cu atom.(2)Magnetization measurements up to 8T in a steady field and up to 40T in a pulsed field are made on a single crystal of NENP containing 3.3 at.% Cu. The magnetization increases rapidly at low fields and becomes saturated above 4T. The magnetization begins to increase again when the magnetic field is increased further. The field dependence of the magnetization at the low field region is quantitatively explained based on the three S=1/2 spins model.(3)Magnetization measurements on S=1 one-dimensional Heisenberg antiferromagnets TMNIN and NINAZ have been performed in a pulsed high magnetic field. The magnetizations are very small in the low field region and begin to increase sharply above the critical fields. This behavior of the magnetization is similar to that observed before in NENP by Katsumata et al. Thus, the existence of the Haldane gap in TMNIN and NINAZ is confirmed experimentally.(4)From an ESR and magnetization measurements on a rapidly grown single crystal of NENP, we have observed the fractional spin degrees of freedom.