X-ray-absorption sum rules in {ital jj}-coupled operators and ground-state moments of actinide ions
- Daresbury Laboratory, Warrington WA44AD (United Kingdom)
- Materials Science Center, University of Groningen, 9747 AG Groningen (The Netherlands)
Sum rules for magnetic x-ray dichroism, relating the signals of the spin-orbit split core level absorption edges to the ground-state spin and orbital operators, are expressed in {ital jj}-coupled operators. These sum rules can be used in the region of intermediate coupling by taking into account the cross term between the {ital j}={ital l}{plus_minus}1/2 ground-state levels and are, therefore, particularly useful in the study of actinides. The calculated expectation values for the ground-state moments of the actinide ions in intermediate coupling show that the spin-orbit-induced operators, such as the magnetic-dipole term, differ strongly from their Hund{close_quote}s rule ground-state values. We also prove the general rule that, when there is a perturbing interaction which is weak compared to the spin-orbit interaction, the ratio of operators with the same total moment remains constant. This condition is usually fulfilled for the crystal-field interaction in the lanthanides and actinides. The values of the ground-state moments as a function of {ital f} count give rise to an interesting trend in the dichroism of the spin-orbit split-core edges. The branching ratio of the 3{ital d} and 4{ital d} circular dichroism signal gradually increases from nearly zero for 5{ital f}{sup 1} to {approximately}0.4 for 5{ital f}{sup 5} and is close to unity for a more than half-filled shell. The unusual behavior of the branching ratio can be related to the higher (lower) value of the magnetic dipole term, {ital T}{sub {ital z}}, for a less (more) than half-filled shell of the actinides in the presence of spin-orbit interaction. Uranium compounds will have a much larger value of {ital T}{sub {ital z}} than the corresponding 4{ital f} compounds. Its precise value can be used as a measure for the {ital f} count. {copyright} {ital 1996 The American Physical Society.}
- OSTI ID:
- 284387
- Journal Information:
- Physical Review, B: Condensed Matter, Vol. 53, Issue 21; Other Information: PBD: Jun 1996
- Country of Publication:
- United States
- Language:
- English
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