-Fe2O3 nanoparticles dispersed in a polymer matrix have been characterized by x-ray diffraction (XRD) and transmission electron microscopy (TEM). The electron paramagnetic resonance (EPR) in 64 Å particles of -Fe2O3 dispersed in a polymer matrix has been investigated in the range 136 - 286 K.
The spin-Hamiltonian parameters and the line widths of Pb3+ in CaCO, have been measured over the temperature range 77 to 300 "K. The hyperfine interaction is very large so that the intermediate field approximation was used. The hyperfine interaction decreases as the temperature increases, in agreement with the effect of lattice-vibrations on the ground state. The hypothesis of a large-amplitude resonance mode is used for explaining the qualitative temperature dependence. Extra line widths is described to the presence of hyperfine interaction of the 207Pb isotope. A dynamic process is assumed which is related to the change of spin-lattice relaxation via phonon modulation of the hyperfine interaction.Utilisant 1'8pproximation du champ intermkdiaire imposee par la forte interaction hyperfine, on a determine pour les ions Pb3+ en calcite irradi6 les parametres de la hamiltonienne de spin et les largeurs de lignes des spectres R E P dans un intervalle de temperature 77 6, 300 "K. On peut conclure sur la decroissance de I'intdraction hyperfine avec ]'augmentation de la temperature, en accord avec l'effet des vibrations du cristal en &tat fondamental. L'hypothhse d'un mode resonant de grande amplitude est employee pour expliquer qualitativement la dependance de temperature. Les rbsultats exphrimentaux indiquent une largeur supplementaire de lignes du spectre R E P pour le isotope de PbZo7. L'existence d'une modulation de l'interaction hyperfine, determinee par, les vibrations du rksean pourrait expliquer un relaxation supplementaire par un process dynamique.
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