MÖSSBAUER SPECTROSCOPY ON NICKEL-ZINC FERRITES

Résumé
La structure magnétique hyperfine du système Zn_xNi_1-xFe₂O₄ (ferrite de nickel et de zinc) a été le sujet de maintes études par effet Mössbauer. Le sujet de cette étude concerne le même type de ferrite avec x égal à 0,3 ; 0,5 et 0,65 à différentes températures en-dessous du point de Néel. On en déduit le temps de relaxation longitudinal en fonction de la température pour les sites d'ions ferriques A et B.

Abstract
The magnetic hyperfine structure of the nickel-zinc ferrite system, Zn_xNi_1-xFe₂O₄, have been the subjects of Mössbauer effect studies for many years /1-6/. It is generally found that the Mössbauer spectra of this material at higher temperature are characterized by the presence of ferromagnetic relaxation /3-6/. Bhargava and Iyengar /6/ fitted the spectra of Ni-Zn ferrites (with x = 0.25, 0.5, 0.75) with the relaxation-shape calculated according to the stochastic model /7/. The calculated line shape agrees with experimental one qualitatively at all temperature except near the Néel point. Here we report our work on the same ferrite with x = 0.3, 0.5 and 0.65 at various temperatures near and below the Néel point. As the result of the successful fitting of the Mössbauer spectra with perturbation theory of Levinson and Luban /8/, we extracted the longitudinal relaxation rates of the A- and B-sites ferric ions in the ferrites as function of temperature.