الفهرس 
1.1.1. Mn–Zn ferritesOnly 14 pages are availabe for public view
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Abstract
The structural, magnetic and electrical properties of mixed Mn-Zn ferrites have been investigated as a function of temperature and composition. The ferrite samples under investigation were classified into three groups, the three groups were prepared by the standard ceramic technique having the formula: 1- The first group Mn1-xZnxFe2O4, (0.0 ≤ x ≤ 0.5; step 0.1) 2- The second group Mn0.9Zn0.1Niy TiyFe2-2yO4; (0.0 ≤ y ≤ 0.25; step 0.05) 3- The third group Mn0.9Zn0.1Ni0.05Ti0.05GdtFe1.9-tO4; (0.0 ≤ t ≤ 0.05; step 0.01) X-ray diffraction (XRD) technique, scanning electron microscope (SEM) and porosity were utilized in order to study the effect of the substitution and its impact on both crystal structure and microstructure. Energy dispersion X-ray analysis (EDX) shows that the estimated stoichiometry is very close to the anticipated values and infrared spectroscopic analysis (IR) for range (200–1000 cm-1) was carried out to investigate the structural characterization of the investigated samples. The molar magnetic susceptibility (χM) for the prepared samples was measured using Faraday’s method in the temperature range (300–650 K) as a function of three different magnetic field intensities of (790, 1100 and 1300 Oe). The initial permeability (μi) was measured from which the Curie temperature (TC) was determined. M-H hysteresis loops using a vibrating sample magnetometer (VSM) were obtained to describe the saturation magnetization (Ms), remanence (Mr) and coercivity (Hc), VSM showed clear a hysteresis curve indicating ferrimagnetic behavior. Moreover, dc electrical resistivity (ρdc) and Seebeck voltage coefficients were measured as a function of absolute temperature using the two probe method. The temperature variation of resistivity exhibits two breaks, each break refers to a change in the activation energy. Seebeck voltage coefficients measurements revealed n-type conduction for all samples. The dielectric constant, dielectric loss factor and ac conductivity for the investigated samples of the three groups were carried out and discussed clearly. The data showed that the dielectric constant, dielectric loss factor increase with temperature and decrease with frequency, while the ac conductivity increased with both temperature and frequency. The conduction mechanism was discussed in view of correlated barrier hopping model (CBH). In first group, the XRD analysis confirms that all samples were prepared in a single–phase cubic spinel structure. The experimental lattice parameter (aexp) was decreased with increasing Zn2+ ions substitution. The crystallite size (L) of samples was found to be in the range (90–115 nm). SEM micrographs showed that the texture was homogenous and their granules were made up of overall crystallite aggregates (20–47μm), the percentage porosity (P%) increased with increase Zn content, dc molar magnetic susceptibility (χM) at room temperature increased up to x = 0.1 and then decreased with increasing Zn2+ ions, while the Curie temperature decreases with increasing Zn content. The dc electrical resistivity exhibits two breaks, each break refers to a change in the activation energy. It was found that, the values of ε’, ε’’ and σac are high for small Zn content (x) and decrease at x ≥ 0.3, the sample x = 0.1 has high magnetic properties and low electric properties more than the above investigated samples. In the second group, it is desirable to improve the electrical properties with maintaining high magnetic properties by substituting Fe3+ ions with Ni2+ and Ti4+ ions together. In the second group, the effect of Ni2+ and Ti4+ ions together on magnetic and electric properties of Mn0.9Zn0.1Niy TiyFe2-2yO4; (0.0 ≤ y ≤ 0.25; step 0.05) was studied. The XRD analysis confirms that all samples in a single–phase cubic spinel structure and the experimental lattice parameter (aexp) was decreased with increasing Ni2+ and Ti4+ ions substitution. The crystallite size (L) of samples was found in the range (108–137 nm), SEM micrographs show that the texture is homogenous structure and their granules were made up of overall crystallite aggregates (15–47 μm). The percentage porosity (P%) increased with increase Ni-Ti content. The dc molar magnetic susceptibility (χM) as well as the Curie temperature decreased with increasing Ni-Ti content. The dc electrical resistivity increased with increasing Ni-Ti content. A decrease in dielectric losses associated with ε’, ε’’ and σac with increasing Ni-Ti content. The sample (y = 0.05) is the optimum investigated sample because it has relatively high magnetic properties and improved electrical properties compared with the parent sample. In the third group, it is desirable to improve the electrical properties with maintain high magnetic properties, it is desirable to retry the enhancement the electric properties with maintain high magnetic properties, this will be done by substituting Fe3+ ion with Gd3+ ion. In the third group, the effect of Gd3+ ion on magnetic and electric properties of Mn0.9Zn0.1Ni0.05Ti0.05GdtFe1.9-tO4; (0.0 ≤ t ≤ 0.05; step 0.01) was studied. XRD analysis revealed that the samples have a cubic spinel (single phase) structure for 0.0 ≤ t ≤ 0.02, while for t ≥ 0.03, a small peak of secondary phase (Gd3Fe5O12) appears and the experimental parameter constant (aexp) initially increases and then decreases with increasing Gd content (t). The crystallite size (L) of samples was found in the range (102–127 nm), SEM micrographs indicate two contrasts corresponding to its respective primary parent spinel phase and the secondary phase (Gd3Fe5O12) for t ≥ 0.03, The percentage porosity (P%) decreased with increase Gd content (t). The saturation magnetization and dc molar magnetic susceptibility at room temperature decreased with increasing Gd content (t). The dc electrical resistivity (ρdc) was found to increase gradually with increasing Gd content (t) from 8.8x103 Ω.m at t = 0.0 to 19.2 x 103 Ω.m at t = 0.05, sample t = 0.01 has a maximum ε’, but for t ≥ 0.02 decreases ε’. Consequently ε’’ and σac have the same trend.