X-Ray Magnetic Circular Dichroism and Structural Model for Co-Doped TiO_2 (Anatase) Thin Film (Condensed Matter : Structure, Mechanical and Thermal Properties)

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We have succeeded in measuring fluorescence X-ray magnetic circular dichroism (XMCD) and absorption spectra at the Co K absorption edge for a small amount of doped Co ions in a Co_xTi_<1-x>O_2 anatase film (x = 0.07 ; 700-Å-thickness) on a LaA1O_3 (001) substrate. X-ray fluorescence intensity was accumulated for 3 d at the pseudo-total-reflection geometry in a synchrotron undulator beamline, BL-39XU at SPring-8. Negative-to-positive dispersion-type XMCD spectra were clearly observed at E=7.725 keV, suggesting the ferromagnetism at room temperature and unlikelihood on the existence of Co-metal clusters. XANES spectra support the Co^<2+> oxidation state and participation of a partial structure of ilmenite-type CoTiO_3. We have proposed a crystal structure of Co-doped anatase films and the ferromagnetic order scheme by Co-Ti-O polysynthetic twin lamellae. A (012) CoTiO_3 layer interstitially distributes parallel to the (001) plane of anatase and replaces a quarter of the anatase cell at intervals of three and half times of the cell along the c axis.
社団法人日本物理学会の論文
2004-04-15