The effect of Fe substitutions by rare-earth ions on magnetic and electrical properties of a Ni-Zn ferrite prepared by the classical method is investigated. A set of seven compounds with formula Ni0.7Zn0.3Fe1.98R0.02O4, where R identical to Yb, Er, Dy, Tb, Gd, Sm or Ce, was prepared. Emphasis is placed on current experimental results of bulk magnetic measurements and transport phenomena. The results obtained reveal that, by introducing a relatively small amount of R2O3 instead of Fe2O3, an important modification of both the structure and the magnetic and electrical properties can be obtained. We explain the influence of the rare-earth ions as an effect of the ionic radius. This assumption is supported by the lattice constant measurements. The best results from the viewpoint of magnetic and electrical characteristic acceptable for high frequencies were obtained for R ions with a large radius and with a stable valence of 3+ such as Gd in our work.

The dielectric parameters are investigated as a function of composition, frequency, and temperature in copper containing ferrites. An "abnormal" behaviour of the dielectric constant is found and also the loss factor as a function of frequency and temperature in comparison with the "normal" behaviour of spinel ferrites. The origin of this abnormal behaviour is attributed to the presence of Cul+ ions which determine the appearance of p-carriers in these ferrites.On a analyse le comportement des parametres dielectriques en fonction de la composition, la frequence et la temperature dans les ferrites qui contiennent du cuivre. On a trouve un comportement "anormal" de la constante diblectrique et du facteur de pertes dielectriques en fonction de la frbquence et la temperature par rapport au comportement ''normal'' pour les ferrites de type spinelle. L'origine de ce comportement anormal eat attribuh &la presence des ions Cul+ qui determinent I'apparition des porteurs de type p dans ces ferrites.

No abstract

No abstract

No abstract