Self-diffusion and free volumes in Nd-Fe-B and Pr-Fe-B permanent magnets

本项目旨在研究稀土金属/过渡金属永磁体Nd_2Fe_（14）B和Pr_2Fe_（14）B的自扩散和原子自由体积。由于晶间熔化发生在超化学计量组成，这些材料作为面向应用的模型系统，以研究准液体晶间膜的扩散行为。由于材料输运行为的高结构敏感性，扩散数据应该产生新的见解的结构上的限制液体层和相邻的液-固界面。此外，这些研究可以阐明这些材料的液相烧结和应力诱导的磁性织构的原子过程，这是实质性的技术相关性。从高温测量的正电子寿命和一致的多普勒展宽的界面自由体积的字符（大小，化学环境）和它们的变化时，晶间熔融转变的具体信息。用于自扩散研究的放射性同位素59 Fe和142 Pr的注入是在共同研究项目的框架内，在波恩大学的Institute für Strahlen- und Kernphysik的离线分离器中进行的。

The present project aims at a combined study of self-diffusion and atomic free volumes in the rare-earth metal/transitionmetal permanent magnets Nd2Fe14B and Pr2Fe14B. Since intergranular melting occurs at hyperstoichiometric compositions these materials serve as application-oriented model system in order to study the diffusion behaviour of quasi-liquid intergranular films. Due to the high structure sensitivity of the material transport behaviour, the diffusion data are supposed to yield novel insight on the structure of confined liquid layers and the adjacent liquid-solid interfaces. In addition, these studies may elucidate the atomistic processes of liquidphase sintering and stress-induced magnetic texturing of these materials which are of substantial technical relevance. Specific information on the character (size, chemical environment) of interfacial free volumes and their variation upon the intergranular melting transition is gained from high-temperature measurements of the positron lifetime and the coincident Doppler broadening. The implantation of the radioisotopes 59Fe and 142Pr for the self-diffusion studies is performed at the off-line separator at the Institut für Strahlen- und Kernphysik of Universität Bonn in the framework of the common research project.