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

本研究计划旨在利用X射线磁性圆二色性（XMCD）方法研究磁性薄膜与吸附分子之间的磁性相互作用。今年，我们在光子工厂建造了一条新的软X射线光束线，其性能比我们以前使用的要高得多。因此，事实证明，即使是非常弱的XMCD信号可以检测到新的光束线。我们开展了以下三个课题。(1)CO和O吸附Co薄膜的Co L-MCD和O K-MCD研究O吸附质的磁性是铁磁性的，而CO吸附质的磁性是反铁磁性的。这一结果表明，吸附位敏感地影响磁性行为。(2)Ni L-MCD和O-K-MCD。结果表明，当Ni厚度小于10 ML时，易磁化轴位于面内，10-50 ML时垂直于面内，50 ML以上时垂直于面内，CO的吸附使垂直磁各向异性（PMA）区域扩展到6 ML ~ 50 ML，CO的感生磁矩在PMA处为铁磁，在面内各向异性处为反铁磁.我们成功地用一个简单的化学键图解释了这些现象。(3)Mn L-MCD的Mn层和氧化的Mn层的Co膜。洁净的Mn与Co之间存在铁磁耦合，而暴露于O_2中只影响Mn，生成MnO，MnO与Co之间存在反铁磁耦合，这些磁性行为取决于吸附分子的种类、吸附位置、磁性膜的厚度等参数。为了更深入地了解分子和金属的化学键，系统的研究是必要的。

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.