Studies on Electronic States of Transition-Metal Compounds and Rare-Earth-Metal Compounds by Spin-Polarized Photoelectron Spectroscopy

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To determine the spin polarization of photoelectrons, a compact low-energy Mott detector was constructed. Its electron-scattering characteristics and instrumental scattering-asymmetry were measured at the scattering angles of <plus-minus>120゜in the incident-electron-energy range from 50eV to 200eV and in the accelerating-voltage range from 15kV to 40kV. The scattering intensity increased with incident-electron energy and decreased with accelerating voltage. This fact shows that this kind of a low-energy Mott detector has an advantage over a high-energy detector operated with a high accelerating voltage over 100kV. By using a gold target, the scattering efficiency of 10^<-4> was obtained and an instrumental scattering-asymmetry was estimated to be less than <plus-minus>3%. These results show that our apparatus is fit enough for practical use.Yb_xLu_<1-x>B_<12> (x=1,3/4, 1/2, 1/4, 0) was adopted as a material to be applied spin-polarized photoelectron spectroscopy. For this alloy system, ordinary photoelectron spectra were measured by using synchrotron radiation. Structures originating from 4f^<14> and 4f^<13> were observed in the spectra; the former appeared just below the Fermi level. As Yb-content is decreased, the intensity of the 4f^<14>-derived structure is abruptly decreased anf the mean valence of Yb becomes close to +3. This suggests that valence fluctuation occurs between Yb^<2+> and Yb^<3+> in this system. Moreover, we decomposed the observed spectra into surface- and bulk-derived spectra by computer-processing.It showed that the mean valence of Yb was 2.4 for the surface and 2.7 for the bulk for samples of high-Yb-content. After this, we plan to advance the analysis of spin-polarized photoemission data and to apply this method to other materials.