الفهرس 
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Abstract
In this study, the physical, magnetic and electrical transport properties of nanoferrites, nanoferroelectric and nanocomposites samples are investigated. The samples are classified into three groups as the following:
1) CFO group consists of CoFe2O4 (CFO), PbZr0.52Ti0.48O3 (PZT), 40%CFO+60%PZT composite and 40%CFO+60%PZT (0-3) core shell (C.S.).
2) CNFO group consists of Co0.1Ni0.9Fe2O4 (CNFO), PbZr0.52Ti0.48O3 (PZT), 40%CNFO+60%PZT composite and 40%CNFO+60%PZT (0-3) core shell (C.S.).
3) NFO group consists of NiFe2O4 (NFO), PbZr0.52Ti0.48O3 (PZT), 40%NFO+60%PZT composite and 40%NFO+60%PZT (0-3) core shell (C.S.).
Ferrites, PZT, composites and C.S. were successfully prepared using sol-gel and hydrothermal methods. XRD diffraction patterns showed that ferrites and PZT had spinel and tetragonal structures respectively. Moreover, XRD showed double phases of ferrite and PZT for composite and C.S. samples. The lattice parameters of the same group showed insignificant change. The lattice parameters (a) and (c) of the constituent PZT in composite and C.S. were lower than the values of its pure form while the tetragonality degree (c/a) showed nearly constant values. The crystallite size of composite and C.S. were larger than their pure forms, ferrite and PZT. Nevertheless, the increase of the crystallite size of ferrites in composite was larger than in C.S. due to the shielding of PZT particles. The values of the microstrain% of constituent phases in C.S. and composite forms were larger than their values in pure forms. Meanwhile, the values of the ferrites microstrian % in C.S. were larger than their correspondence in the composite. HR-TEM was used to distinguish between the microstructure and interconnectivity of the composite and C.S. that was correlated with the microstrain % values. It was recognized that the degree of interconnectivity (interface coupling) could be expressed by the values of the microstrain % of the constituent phases for any composite material. On the other hand, the C.S. samples showed narrower particle size distribution for their constituents than their correspondence in composite. The particle size values were in good agreement with values of the crystallite size. The molecular symmetry was investigated by the FTIR data.
The relative permeability μr was measured as a function of temperature. The μr curve showed two peaks, one at ≈150oC for all groups and the other at Curie temperature TC. The peak at 150oC was attributed to zeroing of the crystal anisotropy. The other peak was due to a transition from ferrimagnetic to paramagnetic. The values of μr are generally small due to the nanosize particles. Moreover, μr(C.S.) > μr(composite) > μr(pure ferrite). These results were ascribed to the porosity, magnetocrystalline anisotropy and microstrain. The Curie temperature TC was determined from the μr(T) curve. It was found that for pure ferrites, the Curie temperature increased from CFO to NFO with CNFO has intermediate value. It was attributed to the decrease in the lattice parameters. The changes of TC in the same group were discussed through the crystallite size. The most important feature of TC results, in any group, is that the Curie temperatures of composite and C.S. are increased relative to TC of pure ferrite.
The magnetic hysteresis loops were measured using VSM, at room temperature, in a magnetic field up to 7kOe. The saturation magnetization Ms of each pure ferrite has the highest value in its group and this was attributed to the chemical composition. On the other hand, Ms of CFO group has the highest values while NFO group has the lowest values. It was ascribed to the fact that the magnetic moment of Co2+ions is higher than that of Ni2+ ions. The composite samples, in each group, revealed the lowest values of Ms. Such behavior was discussed through the formation of Fe2+ which was approved through FTIR. The coercive field Hc, determined from the hysteresis loops, was found to have a direct relation with the anisotropy constant k and an inverse relation with the relative permeability which agrees with Globus model for domain rotation.
The resistivity ρdc was measured as a function of temperature. The ρdc curve showed four regions of conduction for the pure PZT sample with metallic behavior at the first region due to the scattering of electrons. The other regions were interpreted by the p-type extrinsic semiconductor behavior. The ρdc curve for pure ferrite showed three regions of conduction with a semiconducting behavior. The conduction mechanisms of composite and C.S. were consequence of the mechanisms of PZT and ferrites. The resistivity of C.S. came in the second rank after PZT then the composite and pure ferrites. The porosity, stoichiomtery [formation of Fe2+ for ferrites and Pb3+ for PZT], nanosize, microstrain and the interconnectivity parameters played important roles in interpretation of the ρDC)R.T. values. The frequency dependence of the dielectric constant were performed in two frequency ranges (300Hz- 5 MHz) and (1MHz- 3 GHz). The dielectric constant ε′ in the two ranges matched each other, such that the C.S. samples had the highest value within the same group and then PZT, composite and ferrites. The materials showed resonance at the high frequency range (1MHz- 3 GHz) and two self resonant modes TM110 and TM210 appeared at ε′ and observed as absorption peaks at ε′′. The resonance frequencies were affected by the permittivity and the microstructure of the samples. It was found that the C.S. materials have high ε′ with low tanδ at wide range of frequency (300 Hz - 3 GHz) which is suitable for applications. Eventually, by performing the P-E loop experiment, the characteristic ferroelectric hysteresis loop of PZT was observed. Moreover, it was found that the shape of the P-E loop and the hysteresis parameters (Pm, Pr and Ec) values were affected by the resistivity, microstructure and particle size. It was found that the C.S. samples were able to endure high electric field even though the presence of ferrite phase.
Based on the above statement, it is concluded that the (CFO/PZT), (CNFO/PZT) and (NFO/PZT) core shell (C.S.) significantly improve the physical, magnetic and electrical transport properties relative to the standard composite. Such improvement could be utilized in different applications such as sensors, actuators, resonators and multiferroic spintronics devices.