A Study of magnetic grand states in rare earth-transition metal compounds by neutron diffraction technique

由于4f电子与分子场之间的RKKY相互作用通过3d电子的共存和竞争，稀土和过渡金属化合物中的磁性是相当复杂和独特的。尤其是最近，Onodera和他的同事们在具有四方晶体结构的稀土化合物中发现了四极子有序的证据。因此，弄清楚稀土和过渡金属化合物中复杂的磁性是非常有趣的。为了了解稀土化合物的磁性，详细确定其晶体结构和磁性结构是非常重要的。中子衍射法是研究磁性材料静态行为的最有效方法之一。我们在日本原子能研究所的JRR-3M反应堆上建造了新的中子粉衍射仪Hermes。在这个项目中，我们通过科学研究资助项目，成功地改善了爱马仕实验室的实验环境，提高了实验效率。使用Hermes，我们能够确定许多磁性化合物的晶体和磁性结构相图。本项目最重要的结果之一是我们发现了四方化合物DyB_2C_2的磁结构是一种特征的结构：磁矩在c平面上，并且与相邻的磁矩沿c轴垂直。这一特征磁结构表明，RKKY相互作用与qoadrapoler相互作用相互竞争。这一结果对稀土化合物的磁性研究具有重要意义，因为这是DyB_2C_2是第一个经历四极体序的四方化合物的证据。

The magnetism in rare earth and transition metal compounds is quite complicated and characteristic because of the coexistence and/or competition of RKKY interaction between 4f electrons and molecular fields by 3d electrons. In particular, recently, Onodera and his coworkers found evidence of the quadrapoler ordering in rare earth compounds with tetragonal crystal structures. It is, therefore, very interesting to make clear the complicated magnetism in rare earth and transition metal compounds. To understand the magnetic properties in rare earth compounds, it is quite important to decide the crystal and magnetic structures in details. Neutron diffraction technique is one of the most effective methods to make clear the static behavior of magnetic materials. We have constructed the new neutron powder diffractometer, HERMES, at the JRR-3M reactor in Japan Atomic Energy Research Institute. In this project, we have successively improved the experimental circumstance of HERMES and the experimental efficiency by the Grant-in-Aid for Scientific Research. Using HERMES, we were able to determine crystal and magnetic structures phase diagrams in many magnetic compounds. One of the most important results in this project is that we have found that the magnetic structure in the tetragonal compound DyB_2C_2 is characteristic one : the magnetic moments are in the c-plane, and are perpendicular between adjacent ones along c-axis. This characteristic magnetic structure indicates that the RKKY interaction competes with the qoadrapoler interaction. This result is very important in the study of the magnetism in rare earth compounds because this is the evidence that DyB_2C_2 is the first tetragonal compounds which undergoes the quadrapoler ordering.