Determination of the Structure of Lattice Defects by Magnetic Anisotropy

作为原子或裂变反应堆环境材料的材料受到快中子、α、β或原子束的轰击，辐射损伤已成为一个重要问题。目前认为合适的材料是铁基合金，有必要了解铁中缺陷的物理性质。利用磁各向异性、磁化强度和磁畴等磁学技术，研究了快粒子辐照产生的间隙原子的结构和物理性质。首先，建立了宽量程转矩磁力计，对快粒子辐照Fe和Ni单晶产生的感生磁各向异性进行了测量。通过分析所观察到的扭矩曲线，表明在低温下，铁中的晶体结构为110哑铃型，而镍中的晶体结构为100哑铃型。在高温下，铁和镍的晶体分别在（111）面和（110）面上聚集形成团簇环，然后用高压电子显微镜观察电子辐照单晶样品上磁畴壁的运动，发现铁的迁移率比镍的小。实验结果表明，铁间隙原子的体积减小是由于磁矩减小所致，理论上认为间隙原子的情况与高压下材料的情况相似。通过使用模型d带或LMTO带计算，包括磁能，从理论上研究了稳定性和热性质。用这种方法解释了间隙原子的物理性质。研究结果为开发新型反应堆材料合金奠定了基础。

Radiation damages have been an important problem that the materials which are used as the environmental materials for an atomic or a fission reactor are bombarded by fast neutrons, alpha, beta or atom beams. The materials which are considered to be suitable, at present, are iron-base alloys, it is necessary to understand the physical properties of defects in iron. The structure and the physical properties of interstitial atoms which were generated by irradiations of fast particles made clear by using magnetic techniques such as magnetic anisotropies, magnetization and magnetic domains.At first, a wide-range torque magnetometer was constructed, and induced magnetic anisotropy in single crystals of Fe and Ni by fast particle irradiation was detected. By analyzing the observed torque curves it was shown that in low temperatures the structure of interstitials in iron is 110-dumbbell and in nickel 100-dumbbell. At elevated temperatures the interstitials aggregate and form cluster loops on (111) plane in the case of iron and on (110) plane in the case of nickel.Then, by observing the motion of magnetic domain walls on electron-irradiated single crystal specimens by a high voltage electron microscope, it was found that the mobility in iron is smaller than in nickel. From this experiment it is concluded that the volume of an iron interstitial atom becomes small by reducing its magnetic moment.Theoretically, the situation of an interstitial atom is considered to be similar to the case of materials under high pressure. The stability and thermal properties are investigated theoretically by using a model d-band or the LMTO band calculations by including the magnetic energy. The phydical properties of interstitial atoms have been explained by the present method. The results of this study is the base of the development of a new useful alloy for reactor materials.