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

本工作的目标是发展一种新的电子全息原位观察技术，并将这一新技术应用于先进材料中的磁畴研究。主要结果如下：1.研制了一种新型的小霍尔探头装置，使我们能够测量物镜内部的磁场。这种装置揭示了样品附近的磁场与物镜电流之间的关系，从而可以在很大的磁场范围内观察到磁区。2.通过操作安装在电子显微镜中的电磁铁，优化了观察电子全息图的实验条件。建立了全息图中磁信息和电信息(平均内电势的影响)分离的方法。通过对分别在磁性和非磁性状态下获得的两幅数字化全息图的数值分析，可以消除电学信息。4.将新技术应用于钙钛矿型锰氧化物的磁化强度分布的研究，该材料表现出众所周知的巨磁电阻效应。在磁相分离状态下，可以直接观察到磁通的分布。这一结果对理解空穴掺杂锰氧化物的导电机理具有重要意义。

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.