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

本研究的主要课题是利用原子分子吸附和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，这为纳米级磁性的表征提供了一种新的技术。我们发现在功函数阈值附近的紫外磁圆二色性（MCD）显著增强。光发射MCD使我们能够利用光电子发射显微镜（PEEM）观察纳米尺度的磁性，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，限制了该方法的可用性。此外，使用同步加速器辐射的时间分辨能力无法达到亚皮秒（ESRF中的-70 ps），而使用紫外激光很容易克服这一问题。紫外光发射MCD的增强没有被发现，这可能是由于价壳中自旋轨道耦合小导致紫外MCD弱的错误观念和实验发现当光子能量没有正确调谐时紫外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明显增强，这是通过包括自旋轨道耦合在内的简单能带结构计算来证明的。与通常情况下（没有光子能量调谐）相比，增强幅度高达两个数量级，并且Ni薄膜中的MCD对比度高达10%。我们已经构建了紫外MCD PEEM系统，并成功地观察到美丽的磁畴图像。Cu（001）上的cs涂层Ni薄膜。我们现在正在准备飞秒时间分辨装置。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