Europhys. Lett, 48 (2), pp. 233-239 (1999)
Spin density on ligands and covalency of ions in octahedral sites of the garnet:
A polarised neutron diffraction study
V. P. Plakhty 1, A. G. Gukasov 2, R. J. Papoular 2 and O. P. Smirnov 1
1Petersburg Nuclear Physics Institute, RAS - Gatchina, St. Petersburg, 188350,
2Laboratoire Leon Brillouin - CE-Saclay, 911191 Gif-sur-Yvette Cedex, France
(received 31 May 1999; accepted in final form 24 August 1999)
PACS. 75.50Ee - Antiferromagnetics.
PACS. 75.25 - Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies synchrotron-source X-ray scattering, etc.).
PACS. 75.30Et - Exchange and superexchange interactions.
By means of polarised neutron diffraction in an external magnetic field of at the covalent spin density is unambiguously observed on the ligands of the ions that occupy only the octahedral 16a sites in the antiferromagnetic garnet. The maximum entropy method is used to reconstruct these spin density peaks. The moment value of the field-induced component is found by the least-squares refinement on the flipping ratios of the reflections affected only by oxygen. The ligand moment is determined to be by extrapolation of this component to the spin-flip (exchange) field. The corresponding reduction of the moment is 14(2)%. An impurity moment of in 24c sites (probably 0.21% of ) can explain the partial magnetic disorder of this material.
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