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

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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