We have studied the effect of Sr doping on the magnetic structure of La1-x
Sr
x
CoO3 (x=0, 0.2, 0.3, 0.4, 0.5 and 0.6) by X-ray magnetic circular dichroism (XMCD) at Co K absorption edges. A negative XMCD peak was clearly observed for pure LaCoO3 at E=7.719 keV within the threshold region of the main edge, suggesting the existence of the intermediate-spin state of Co3+. A positive XMCD peak appeared at E=7.723 keV by Sr substitution of La in LaCoO3 (x≥0.2) in accordance with the low-spin state of Co4+ and X-ray absorption near-edge-structure (XANES) spectra. A negative XMCD peak was also observed at the pre-edge, which can be explained as the hybridization with the neighboring Co4+ in the dipole transition. The dispersion-type XMCD signals at the main edge may be rationalized with the hypothetical double-exchange interaction between Co3+ and Co4+.
The absorption spectrum of O2 has been photographed in the argon continuum region with a 3-m vacuum spectrograph at a dispersion of 1.42 Å/mm. Based on the known rotational constants of the ground state, the rotational constants of the upper states have been determined for Tanaka progession (I), β–X3Σg−, progression (II), α1Σu+–X3Σ−, and those of a new band at 1144.6 Å. In a brief discussion of the upper electronic states, it is suggested that both the β state and the upper states of the 1144.6 Å band are 3Σu+ states and their electron configurations are (πg2p)(3pπ) and (πg2p)(4pπ), respectively, and also the α state is (πg2p)(3pπ)1Σu+.
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 x Ti 1Àx O 2 anatase film (x ¼ 0:07; 700-# A-thickness) on a LaAlO 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 ¼ 7:725 keV, suggesting the ferromagnetism at room temperature and unlikelihood on the existence of Cometal clusters. XANES spectra support the Co 2þ 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.
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