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

点击翻译按钮获取中文摘要

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.