X-ray resonant scattering of (004n+2) forbidden reflections in spinel ferrites
- Instituto de Ciencia de Materiales de Aragon, CSIC-Universidad de Zaragoza, Plaza. San Francisco s/n, 50009 Zaragoza (Spain)
- CEA-Departement de Recherche Fondamentale sur Matiere Condensee, SP2M-Nanostructures et Rayonnement Synchrotron, 17 Avenue des Martyrs, 38042 Grenoble (France)
- Laboratoire de Cristallographie, C.N.R.S., BP-166, 38042 Grenoble Cedex 09 (France)
The origin of the x-ray resonant scattering of (002) and (006) forbidden reflections in the spinel ferrites has been investigated. Resonant features were previously observed in Fe{sub 3}O{sub 4} at the pre-edge and main-edge energies of the Fe K-absorption edge. They were ascribed to dipole-quadrupole and dipole transitions at the tetrahedral and pseudo-octahedral Fe ions, respectively. To corroborate this origin and to differentiate between effects at the different metal sites, we have studied the energy and azimuthal dependencies of these reflections at the Fe, Co, and Mn K edges in MnFe{sub 2}O{sub 4} and CoFe{sub 2}O{sub 4} spinels. Mn{sup 2+} mainly replaces Fe in the tetrahedral site whereas Co{sup 2+} occupies the octahedral site. No pre-edge peak is observed either at the Fe K-edge in MnFe{sub 2}O{sub 4} or at the Co K edge in CoFe{sub 2}O{sub 4}. On the other hand, the peak at the absorption edge and the oscillations at energies beyond the edge are observed at the Fe K edge in MnFe{sub 2}O{sub 4} and CoFe{sub 2}O{sub 4} and at the Co K edge in CoFe{sub 2}O{sub 4}. Therefore, the pre-edge peak comes from the metal ions at the tetrahedral site while the main-edge peak arises from the metal ions at the pseudo-octahedral site of the spinel structure. The azimuthal dependence and the energy line shape confirm the dipole-quadrupole and dipole characters of these pre-edge and main-edge resonances, respectively. The energy-dependence spectra of Fe{sub 3}O{sub 4} above and below the Neel temperature are alike, discarding any magnetic effect on the resonant spectra. Finally, the fine structure at energies beyond the absorption edge has been theoretically simulated considering only the local anisotropy of the dipolar atomic scattering factor of the pseudo-octahedral metal atom. These results demonstrate that (004n+2) resonant reflections arise from the anisotropy of the local structure around the transition-metal atom without contributions of charge or d-orbital ordering.
- OSTI ID:
- 20664922
- Journal Information:
- Physical Review. B, Condensed Matter and Materials Physics, Vol. 70, Issue 15; Other Information: DOI: 10.1103/PhysRevB.70.155105; (c) 2004 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1098-0121
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ABSORPTION SPECTROSCOPY
ANISOTROPY
COBALT IONS
COBALT OXIDES
DIPOLES
ENERGY DEPENDENCE
FERRITES
FINE STRUCTURE
IRON IONS
IRON OXIDES
K ABSORPTION
MANGANESE COMPOUNDS
MANGANESE IONS
NEEL TEMPERATURE
RESONANCE SCATTERING
SPINELS
X RADIATION
X-RAY DIFFRACTION
X-RAY SPECTROSCOPY