M-edge x-ray absorption spectroscopy of 4f instabilities in rare-earth systems (invited)
Soft x-ray absorption spectroscopy in the M-edge region is explored as a tool for studying 4f instabilities. The quasiatomic M/sub IV,V/ spectra, recorded by total-electron yield under UHV conditions, carry information on the initial-state 4f occupancy. For compounds of the heavy rare earths, even at high dilution (e.g., Tm/sub 0.05/Y/sub 0.95/Se), mean valences can be derived, which agree with those from lattice-constant systematics (e.g., for TmSe and Sm/sub 0.3/Y/sub 0.7/S). A moderate surface sensitivity allows the observation of surface-induced valence changes on EuPd/sub 3/, TmS, and SmAl/sub 2/. The M/sub IV,V/ spectra studied for 10 Ce compounds fall in two categories: pure 3d/sup 9/4f/sup 1/ final-state multiplets for ..gamma..-like compounds, and additional peaks at about 5 eV higher energies for ..cap alpha..-like and intermediate systems. With increasing intensity of the satellites, which are assigned to 3d/sup 9/4f/sup 1/ final states, the 3d/sup 9/4f/sup 2/ multiplet structure gets washed out. An interpretation of the spectra with the recent Anderson-impurity theory of Gunnarsson and Schoenhammer leads to 4f occupancies greater than 0.7, even in extreme ..cap alpha..-like systems. In addition, M/sub III/-edge spectra exhibit one peak in ..gamma..-like and two peaks in ..cap alpha..-like and intermediate Ce systems, which are assigned to 3p/sup 5/4f/sup 1/ and 3p/sup 5/4f/sup 0/ final corestates. With increasing ..cap alpha..-like character, the 4f/sup 1/ peak is found to move to higher energies presumably due to a decrease in 4f screening with increasing 4f hybridization.
- Research Organization:
- Freie Universitaet Berlin, D-1000 Berlin 33, Germany, and Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720
- OSTI ID:
- 5195618
- Journal Information:
- J. Appl. Phys.; (United States), Vol. 55:6
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
SUPERCONDUCTIVITY AND SUPERFLUIDITY
74 ATOMIC AND MOLECULAR PHYSICS
RARE EARTH COMPOUNDS
ABSORPTION SPECTROSCOPY
ELECTRONIC STRUCTURE
ABSORPTION SPECTRA
HYBRIDIZATION
VALENCE
X-RAY SPECTROSCOPY
SPECTRA
SPECTROSCOPY
656000* - Condensed Matter Physics
640302 - Atomic
Molecular & Chemical Physics- Atomic & Molecular Properties & Theory