الفهرس 
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Abstract
In the present study, two groups of Ni-Zn nanoferrite compositions were prepared by coprecipitation method and calcined at different temperatures. The replacing of Ni ions by Zn or Ca ions lead to improve some physical properties of such ferrites in order to enhance its electronic applications.In section one , group one, the ferrites have the formula Ni1-xZnxFe2O4(0.0£x£1.0) were prepared and characterized. X-ray diffraction (XRD) and FTIR analysis confirm the presence of single phase cubic spinel structure. The process that amorphous precursors translated to crystalline ferrite was confirmed by means of Differential Scanning Calorimetry and Thermogravimetric Analysis
(DSC-TGA). Scanning Electron Microscope (SEM) and Atomic force microscopy (AFM) assure that all samples have nano-crystalline scale. The values of crystallite size of all prepared samples of Ni1-xZnxFe2O4 (0.0£x£1.0)nanocomposites which calculated from the most intense peak (311) by the Debye-Scherrer formula ranged from 4.1 nm to 210 nm. The crystallite size found to be decreased with increasing Zn2+content whileas it increased with calcination temperature.AC conductivity was carried out in frequency range from 100 kHz up to 5 MHz and in temperature range from 300 K up to 750 K for all studied samples. The acconductivity, σac , was found to be increases with both temperature and frequency. The values of ac conductivity ranged from 10-3-10-7 W-1 cm-1 which confirm the semiconductor behavior for all samples. The addition of Zn2+ decrease σac up to x=0.3 for sample calcined at 1000 oC. The calculated values of activation energies mainly increase with Zn2+ content and sintering temperature at relatively low and high temperature ranges. The dependence of σac on frequency is governed by the relation σac = Aωs. The calculated values of s were decreases with increasing temperature for all studied samples. In the temperature range from 300 to 550 K the values of s decreases from 1 to about0.5 confirming the polaron hopping conduction mechanism. Whereas the values
of s lie between 0.5 to about 0.1 in the temperature range 550 – 750 K
confirming the ionic diffusion of Ni ions. The dielectric constant ε’ and
dielectric loss ε’’ were measured for all samples and found to be obeying Debye
dispersion relation in wide range of frequencies and temperatures. The dielectric
constants were lower than those normally reported for microscale Ni-Zn ferrite.
Using Cole-Cole diagram for composition Ni0.7Zn0.3Fe2O4, the dipole relaxation
times, τ , were carried out. Also, the values of optimum hopping distance, R,
were calculated.
All prepared Ni-Zn nanoferrite, showed narrow hysteresis loops which
confirm the soft ferrites nature of such composition. The saturation
magnetization, Ms , for all prepared samples was measured at room temperature.
The addition of Zn2+ increases the values of saturation magnetization up to 70.8
emu/g for sample Ni0.7Zn0.3Fe2O4, x=0.3, calcined at 1000 oC. While the
coercivity had a reverse trend for all samples.
The addition of some element such as Ca which have atomic radius
bigger than that of both Ni and Zn ions, may be enhances both electrical and
magnetic properties of such ferrite. Also, replacing the multivalent Ni ions by
univalent Ca ions may enhance also these properties. So ferrites have formula
Ni0.7-yZn0.3CayFe2O4 (0.0£y£0.7) were prepared (group two).
In section two, (group two), the ferrites have the formula
Ni0.7-yCayZn0.3Fe2O4 (0.2£y£0.7) were prepared and characterized.
X-ray diffraction (XRD) and FTIR analysis confirm the presence of single phase
cubic spinel structure. The process that amorphous precursors translated to
crystalline ferrite was confirmed by means of DSC, TG, SEM and AFM assure
x
also, that all samples have nano-crystalline scale. The values of crystallite size
of all prepared samples of Ni0.7-yCayZn0.3Fe2O4 (0.0£y£0.7) nanocomposites
which calculated from the most intense peak (311) by the Debye-Scherrer
formula ranged from 8.5 nm to 100 nm. The crystallite size found to be
decreased with increasing Ca2+content while it increased with calcination
temperature.
AC conductivity was carried out in frequency range from 100 kHz up to
5 MHz and in temperature range from 300 K up to 750 K for all studied
samples. The ac conductivity, σac , was found to be increases with both
temperature and frequency. The values of ac conductivity ranged from 10-6-10-8
W-1 cm-1 which confirms the semiconductor behavior for all samples. The
addition of Ca2+ decrease σac up to y=0.3 for sample calcined at 1000 oC. The
calculated values of activation energies mainly increase with Ca2+ content and
sintering temperature at relatively low and high temperature ranges. The
dependence of σac on frequency is governed by the relation σac = Aω
s. The
calculated values of s were decreases with increasing temperature for all studied
samples. In the temperature range from 300 to 550 K the values of s decreases
from 1 to about 0.5 confirming the polaron hopping conduction mechanism.
Whereas the values of s lie between 0.5 to about 0.1 in the temperature range
550 – 750 K confirming the ionic diffusion of Ni ions. The dielectric constant ε’
and dielectric loss ε’’ were measured for all samples and found to be obeying
Debye dispersion relation in wide range of frequencies and temperatures. The
dielectric constants were lower than those normally reported for microscale
Ni-Zn-Ca ferrite. Using Cole-Cole diagram for composition
Ni0.4Zn0.3Ca0.3Fe2O4, the dipole relaxation times, τ, were carried out. Also, the
values of optimum hopping distance, R, were calculated.
xi
The addition of Ca2+ reduces the electrical conductivity and dielectric
loss comparing with the parent ferrites. This reduction in these parameters can
be control the eddy current which results in energy consuming.
All prepared Ni-Zn-Ca nanoferrite, showed narrow hysteresis loops
which confirm the soft ferrites nature of such composition. The saturation
magnetization, Ms , for all prepared samples found to be decreases mainly with
increasing Ca2+ content. Whileas the addition of Ca2+ enhances mainly the
coercivity up to y=0.3.
All the above results suggest that, the investigated nanoferrites can be
use at higher frequencies than the corresponding NiZn and NiCaZn
microferrites.