الفهرس 
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Abstract
The ferrite samples under investigation were classified into two main groups. The first one is pure Mn Zn-ferrite according to general formula Mn1-xZnxFe2O4 , where 0.1 ≤ x ≤ 0.7, while the second group is Mn-Zn-ferrite doped with different rare earth element (Dy , Gd ,Sm ,Nd and Ce) according to the formula Mn0.6Zn0.4 RyFe2-yO4 where y=0.02. All samples were prepared by the standard ceramic technique. The measurements were carried out before and after laser irradiation. The X-Ray and FTIR measurements, electric measurements, Seebeck measurements, photo Galvano-magnetic effect, were carried out before and after laser irradiation. First group: 1-The X-ray diffraction patterns of Mn1-xZnxFe2O4 ferrites confirm that the samples were formed in a single phase cubic structure and no external lines were detected as compared with ICDD card no (74-2402). By increasing Zn content, the lattice parameter and porosity decreased and X-ray density increased. 2- The data of IR transmittance spectra gives four fundamental active bands, designated υ1, υ2, υ3 and υ4, where υ1, υ2 indicate the high frequency bands and υ3, υ4 are the low frequency ones, reveal the formation of spinel structure. 3- The dielectric constant (ε/) and the dielectric loss factor (ε//) were measured as a function of temperature and applied frequencies. The data of (ε/) show an increase with temperature and (ε//) has nearly the same trend for all samples. 4- The variation of ac electrical conductivity (ln σ) as a function of the reciprocal of absolute temperature at different frequencies is reported. The data give more than one straight line with different slopes indicating different conduction mechanisms. The hopping model is the most predominant one. 5- Seebeck voltage coefficient was measured, the obtained data show that the sign of the Seebeck coefficient is negative for all ferrites under investigation except (x=0.4). A critical concentration of Zn ions at which the sample has lowest conductivity is Mn0.6Zn0.4Fe2O4. Second group: Samples of the general formula Mn0.6Zn0.4 RyFe2-yO4, where R= (Dy, Gd, Sm ,Nd and Ce) and y=0.02 were prepared. The measurements in the second group were carried out before and after laser irradiation using Nd-Yag laser with (λ=1064 nm). from X-ray analysis, it is observed that the samples crystallized in a spinel structure of cubic symmetry as compared with ICDD card number (74-2402). Laser irradiation increases the crystal size of the samples and decreases the dielectric constant and dielectric loss factor. After laser irradiation the conductivity decreased for all rare earth substituted samples irrespective of the type of rare earth used except Sm3+ one.