Optical Microscopic Faraday Rotation Study on Magnetization Relaxation in the Spin Systems Having Ordered Structures with Non-trivial Degeneracy

在具有竞争相互作用的凝聚态中，样品中的不均匀性干扰了对多简并有序态动静态性质真实特征的观察。为了克服这个困难，我们已经开发了一个新的实验系统，测量磁化强度和它的长时间衰减的均匀区域通过显微镜提取。本研究计画为期三年，主要任务是建构一套配备超导磁铁的光学仪器，以量测磁光效应，如法拉第旋转及光学双折射，并使用光学显微镜进行量测。最终的目标是将这两个系统连接在一起。虽然前者已经开始运行，但后者才刚刚建立。另一方面，与本研究相关的几个研究项目也取得了重要成果。在具有类伊辛相互作用的混合化合物Fe_ MG_xCl_2中<1-x>，由于无规场效应，可以表征出剩磁的长时间衰减和自旋玻璃行为。此外，作为竞争体系所固有的新问题，从各相的磁结构和连续相变的机制方面阐明了六方层状MnX_2（X=Br，I）中伴随着一级相变的连续相变。在KNICl_3型晶格中发现了铁电性，空间群为P6_3cm。后者的发现开辟了一个新的范式，其中反映反铁磁性和铁电性共存的物理引起了相当大的关注。用超导磁体的实验系统成功地测量了三角形晶格反铁磁体RbMnBr_3和竞争相互作用的层状磁体NiBr_2的磁相图。这样，我们需要进一步努力才能完成我们的项目。然而，本项目的前景是相当广阔的。

In condensed matter with competing interactions, inhomogeneity in specimens disturbs observation of true feature of dynamic and static properties of their multi-degenerate ordered states. To remove this difficulty, we have developed a new experimental system measuring magnetization and its long time decay on a homogeneous region extracted by means of a microscope. For the term of this research project over three years, the main task was to construct an apparetus equiped with a superconducting magnet for optical access for measuring magneto-optical effects, such as Faraday rotation and optical birefringence and to do that with an optical microscope. The final aim was to link those two systems together. Although the former system has already been operated, the latter is just settled recently.On the other hand, a couple of research programs associated with this study bring about important results. In a mixed compound with Ising -like interaction, Fe_<1-x>MG_xCl_2, long time decay of remanent magnetization due to the random field effect and spin glass behavior could be characterized. Furthermore, as new problems inherent to competing systems, the successive phase transition accompanied with the first order transition in hexagonal layr type MnX_2(X=Br, I)were clarified with respect to magnetic structures of each phase and a mechanism of successive transition. Ferroelectricity was found in the KNICl_3 type lattice with the space group P6_3cm. The latter finding opened a new paradigm in which the physics reflecting coexistence of antiferromagnetism and ferroelectricity is attracted considerable attention. Experimental system with superconducting magnet was succeeded in measuriong the magnetic phase diagram of a triangular lattice antiferromagnet RbMnBr_3 and a layr type magnet with competing interactions NiBr_2. In this way, it takes further effort to fulfilll our project. However the prospect of the present project is rather widely opened.