Development of observation methods for nano-sized magnetic domains with electron holography

本文的目标是发展一种新的电子全息原位观测技术，并将新技术应用于先进材料的磁畴研究。研究结果总结如下：1。研制了一种带有小霍尔探头的新型仪器，使我们能够测量物镜内的磁场。该装置揭示了试样附近的磁场与物镜电流之间的关系，从而可以在较宽的外加磁场范围内观察到磁畴。通过操作安装在电子显微镜上的电磁铁，优化了观察电子全息图的实验条件。全息图的可见性大大提高。建立了一种将全息图中的磁信息与电信息（平均内电位的作用）分离的方法。通过对磁性和非磁性两种状态下的数字化全息图进行数值分析，可以消除电信息。将新技术应用于钙钛矿型锰矿石的磁化分布研究，该锰矿石具有众所周知的巨磁阻。直接观察了磁相分离状态下的磁通量分布。这一结果有助于理解掺杂孔洞的锰酸盐的导电机理。

The target of the present works is to develop a new technique of in situ observations with electron holography and apply the new techniques to studies of magnetic domains in advanced materials. The results are summarized as follws:1.A new apparatus with a small hall probe was developed, which enables us to measure the magnetic field inside the objective lens. This apparatus has revealed the relation between the magnetic field near the specimen and the electric current of the objective lens so that magnetic domains can be observed in a wide range of the applied magnetic field.2.Experimental conditions to observe electron holograms were optimized by operating the electromagnets installed in the electron microscope. Visibility of the holograms was much improved.3.A technique to separate the magnetic information in holograms from the electric information (the effect of mean inner potential) was established. The electric information can be eliminated by numerical analyses of two digitized holograms, which are obtained in magnetic and nonmagnetic states, respectively.4.The new techniques were applied to studies of magnetization distribution in a perovskite-type manganite, which exhibits the well-known colossal magnetoresistance. Distribution of magnetic flux was directly observed in a magnetically phase-separated state. The results shed light on understanding of the conduction mechanism of hole-doped manganites.