Surface chemical control and characterization of magnetism of nano-scale thin films, wires and clusters

本研究的主要内容是通过原子和分子吸附、表面反应等表面化学技术来控制磁性薄膜、纳米线和纳米团簇的磁性。特别是从微观角度研究了吸附引起的自旋重取向转变。在整个项目中，我们发现了一个新的重要现象，这为纳米尺度的磁性提供了一种新的表征技术。我们发现，在功函数阈值附近，光电发射的紫外磁二向色性(MCD)有了惊人的增强。利用光电子发射显微镜(PEEM)可以观察到纳米尺度的磁性，其典型的特殊分辨率为10~40 nm。通常，MCD PEEM测量是使用第三代同步辐射软X射线作为光源进行的，这限制了这种方法的可用性。此外，使用同步…的时间分辨率更多的强子辐射不能达到亚皮秒(在ESRF中为-70ps)，这很容易通过使用紫外线激光来克服。紫外光发射MCD的增强没有被发现的事实可能归因于错误的预先概念，即UV MCD是由于价层中小的自旋-轨道耦合而弱的，以及实验发现当光子能量不正确时UV MCD实际上是弱的。在本研究中，我们发现Fe、Co和Ni薄膜的紫外光发射MCD有显著的增强，这是通过包括自旋-轨道耦合在内的简单的能带结构计算来证明的。与通常的情况(无光子能量调谐)相比，增强幅度高达两个数量级，镍薄膜的MCD对比度高达10%。我们已经构建了紫外MCD PEEM系统，并成功地观察到了美丽的磁畴图像。在铜(001)面上镀有CS涂层的镍膜。我们现在正在准备一台飞秒时间分辨装置。较少

The main subject of the present research is to control the magnetism of magnetic thin films, nanowires and nanoclusters by means of surface chemical techniques such as adsorption of atoms and molecules and surface reactions. Especially, adsorption induced spin reorientation transitions have been investigated from the microscopic point of view. Throughout this project, we discovered a novel important phenomenon, which provides a new characterization technique for nanoscale magnetism. We have found surprising enhancement of the ultraviolet magnetic circular dichroism (MCD) of the photoemission near the work function threshold. The photoemission MCD allows us to observe nanoscale magnetism using photoelectron emission microscopy (PEEM), whose typical special resolution is 10〜40 nm. Usually, MCD PEEM measurements have been performed using third-generation synchrotron radiation soft x rays as a light source, limiting the availability of this method. Moreover, time-resolving power using sync … More hrotron radiation cannot reach subpicosecond (-70 ps in ESRF), which is easily overcome by using ultraviolet lasers. The fact that the enhancement of the UV photoemission MCD was not discovered may be attributed to the poor preconcept that the UV MCD is weak due to small spin-orbit coupling in the valence shell and to the experimental finding that the UV MCD is actually weak when the photon energy is not tuned correctly. In the present study, we found noticeable enhancements of the UV photoemission MCD from Fe, Co and Ni films, which were justified by means of simple band-structure calculations including spin-orbit couplings. The enhancements are as much as two orders of magnitude compared to the usual condition (no photon energy tuning), and the MCD contrast in Ni films amounts as much as 10%. We have constructed UV MCD PEEM systems and have successfully observed beautiful magnetic domain images in. Cs-coated Ni films on Cu(001). We are now preparing a femtosecond time-resolving setup. Less