الفهرس 
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Abstract
In the present thesis, the study of some structural, elastic, thermal, mag-netic, and electrical properties for a series of the as-prepared nanosamples of stoichiometric Co-Ag ferrites with the chemical compositions Co1−2xAgxFe2+xO4 (x = 0, 0.002, 0.004, 0.006, 0.008, 0.01, 0.02, and 0.03) prepared by the citrate precursor auto-combustion method has been performed. Also, the physical properties of the nanocomposite samples (1−Y)(ZnO)/Y(Co1−2xAgxFe2+xO4) prepared by the chemical co-precipi-tation method have been studied, where these nanocomposite samples have been divided into two groups. The first group (G1) includes x = 0.02 and Y = (0.1, 0.3, and 0.5), while the second group (G2) includes x = 0.03 and Y = (0.1, 0.3, and 0.5). Moreover, the usability of all the prepared samples as antibacte-rial materials has been investigated, where the antibacterial activity of the fer-rite samples with their corresponding composite counterparts has been com-pared. A detailed study has been conducted on all the nanosamples using the X-ray diffraction (XRD) technique, confirming the single spinel phase FCC struc-ture of all the Co-Ag ferrite samples. The characteristic peaks of the spinel ferrite and ZnO phases manifest in the composite samples. The samples’ crys-tallite size, lattice parameter, measured density, X-ray density, porosity, and specific surface area have been determined. The average particle sizes of the investigated samples, estimated by the particle size analyzer (PSA), have a wide distribution in the nanoscale in which the crystallite size D(311) values are included in this range. The transmission electron microscopy (TEM) images of the Co-Ag ferrite nanoparticles confirms their cubical shape. Moreover, it confirms that the nanoscale sizes of Co-Ag ferrites and the corresponding IV Abstract nanocomposites are in good agreement with the results of the PSA. The se-lected area electron diffraction SAED shows spotty ring patterns, revealing the crystalline structure of the nanoferrite and composite samples. In all the investigated samples, the structure has been analyzed by Fourier transform infrared (FTIR) spectroscopy and shows the two prominent absorp-tion bands v1 and v2, which are usually attributed to the tetrahedral and octahe-dral of the spinel lattice, respectively. In addition to these absorption bands, the stretching vibration of the Zn2+-O-2 has been observed for nanocomposite samples. Debye temperature and elastic moduli have been calculated for the nanoferrite samples. Thermal properties have been investigated for Co-Ag fer-rites and the corresponding nanocomposites. The magnetic parameters of all the investigated samples, such as saturation magnetization, coercivity field, and remnant magnetization, have been estimated using a vibrating sample magnetometer (VSM). The magnetic behavior of the investigated samples has been explained depending on the simultaneous influence of several factors such as density, grain size, and cation distribution. The electrical properties of all the investigated samples, such as dc conductivity, ac conductivity, dielectric constant, dielectric losses, and loss tangent, have been determined as a function of frequency, temperature, and composition. The electrical modulus and im-pedance spectroscopy have been analyzed to understand the electric behavior of the Co-Ag ferrites and their nanocomposite samples. The evaluation of the antibacterial activity of Co-Ag ferrites nanosamples has been performed by the Kirby-Bauer disk diffusion test. The Co-Ag ferrite NPs with Ag content of x = 0.008, 0.010, 0.020, and 0.030 exhibited good antibacterial activity against tested reference strains and clinical isolates. The broth dilution method was also used to identify the lowest concentration of the Co-Ag ferrite NPs and their nanocomposite counterparts that inhibit bacterial Abstract V growth against reference strains (E. coli ATCC 25922 and S. aureus ATCC 29213) and multidrug-resistant clinical (E. coli and S. aureus), while the inhi-bition of bacterial growth against the Pseudomonas aeruginosa (P. aeru-ginosa), and Enterococcus faecalis (E. faecalis) isolates was only studied in the case of the composite samples which have exhibited interesting antibacte-rial activity results In the broth dilution method, the ferrite NPs with Ag con-tent of x = 0.008, 0.010, 0.020, and 0.030 have exhibited good antibacterial activity against the tested reference strains and clinical isolates. Also, the nano-composite samples have shown antibacterial activity better than their pure nanoferrite counterparts, particularly the nanocomposite sample of (x = 0.02, Y = 0.3, and x = 0.03, Y = 0.5). Finally, antimicrobial activity by growth curve method was performed on the nanocomposite samples, and significant retardation in the growth of either (E. coli or S. aureus) reference strain has been observed in the presence of 100 μg//mL of x = 0.02, Y = 0.3. The scanning electron micrographs (SEM) have revealed the harmful effect of the selected sample of Co-Ag ferrite of x = 0.03 and its nanocomposite counterpart (x = 0.03, Y = 0.5) against (S. aureus and E. coli), presenting characteristic morphological cell changes confirming the efficiency of the prepared nanosamples as promising antibacterial materials.