Synthesis and Orbital structure of structure- and valence-controlled layered manganites

在本项目中，我们系统地合成了结构控制和价控制的层状锰矿石，并研究了它们的磁输运性质以及磁性和晶体结构。下面，我们列出了在这个项目中取得的主要成果。在该体系中，我们可以通过化学取代来控制(a) Mn离子的形式价态和(b) Mn06八面体的畸变。经过系统的晶体合成和物理性质的测量，我们实验推导出了双层锰矿石的基态相图。我们进一步发现磁性结构与Mn06八面体的畸变之间有很强的相关性。轨道稳定性与磁结构的关系我们通过计算马德隆势能来评价轨道稳定性。我们清楚地观察到，在固定Mn价（= +3.4）下，结构控制的双层锰的轨道稳定性与磁性结构之间存在很强的相互关系。因此，在双层锰中，化学取代会影响轨道的稳定性。与其他过渡金属氧化物体系形成鲜明对比。轨道的直接观察（与Sakata组合作）最近，我们成功地利用名古屋大学Sakata组开发的MEM技术，对双层锰的轨道状态进行了可视化。我们计划在这段时间启动一个项目，即轨道物理，并获得一些研究基金。

In the present project, we have systematically synthesized structure- and valence-controlled layered manganites, and have investigated their magnetotransport properties as well a magnetic and crystal structures. In the following, we list a major results obtained in this project.1. Ground state phase diagram for bilayer manganitesIn this system, we can control (a) formal valence of the Mn ions and (b) distortion of the Mn06 octahedra by means of chemical substitution. After a systematical crystal synthesis and measurements of their physical properties, we have experimentally derived the ground state phase diagram for bilayer manganites. We further have found a strong correlation between the magnetic structure and distortion of the Mn06 octahedra.2. Interrelation between orbital stability and magnetic structureWe have evaluated the orbital stability by calculation of the Madelung potential energy. We clearly have observed strong interrelation between the orbital stability and magnetic structure in the structure-controlled bilayer manganites at a fixed Mn valence (= +3.4). Therefore, in the bilayer manganites, chemical substitution affects the orbital stability. Making a sharp contrast with the other transition metal oxide systems.3. Direct observation of the orbital (in collaboration with Sakata group)We recently have succeed in visualizing the orbital state of bilayer manganites by means of MEM, which was developed by Sakata group at Nagoya University. We plan to start a project on this time, that is orbital physics, with getting some research fund.