Study of X-ray magnetic circular dichroism in magnetic chemistry and surface chemistry

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The purpose of this research proposal is to investigate the magnetic interaction between magnetic thin films and adsorbed molecules by use of the X-ray Magnetic Circular Dichroism (XMCD) method. In this year, we have constructed a new soft x-ray beamline in the Photon Factory, whose performance is much higher than that we used before. Thus, it turned out that even very weak XMCD signal can be detected with the new beamline. We have carried out following three subjects.(1) Co L-MCD and O K-MCD study of O and CO adsorbed Co thin films. The magnetism induced by O adsorbate is ferromagnetic, but that induced by CO is antiferromagnetic to the substrate Co magnetism. This result suggests that the adsorption site sensitively affect the magnetic behavior.(2) Ni L-MCD and O K-MCD of CO adsorbed Ni thin films. It is known that the magnetic easy axis is in plane in the Ni thickness of less than 10 ML, and perpendicular in the range of 10-50 ML, and again in plane above 50 ML.It was revealed that CO adsorption extends the region of perpendicular magnetic anisotropy (PMA) to 6 ML-50ML.Furthermore, the induced magnetic moment of CO is ferromagnetic at PMA, and antiferromagnetic at the in plane anisotropy. We succeeded in interpreting these phenomena by a simple chemical bonding scheme.(3) Mn L-MCD of Mn layer and oxidized Mn layer on Co films. Clean Mn has a ferromagnetic coupling with Co, but the exposure of O_2 only affects Mn and MnO is formed, which has, in turn, antiferromagnetic coupling with Co.These magnetic behaviors depend on many parameters such as the kind of adsorbed molecules, adsorption site, thickness of magnetic films. Systematic study is necessary to get a deeper insight in chemical bonding of molecules and metals.