Thesis & Dissertations

This work investigated the effect of different nanosized ferrites (ZnFe2O4 and CoFe2O4) addition on mechanical and magnetic properties of Gd-123 superconducting phase. Nanoferrites were synthesized by Co-precipitation method and characterized using X-ray powder diffraction (XRD), transmission electron microscope (TEM) and magnetic hysteresis measurements. Superconducting samples of type (ZnFe2O4)xGdBa2Cu3O7-δ and (CoFe2O4)xGdBa2Cu3O7, with 0.00 ≤ x ≤ 0.40 wt. % were prepared by the conventional solid-state reaction technique and characterized using XRD, scanning electron microscopy (SEM) and ion beam analysis. XRD results indicate that Gd-123 maintained its orthorhombic structure regardless of the nanosized ferrites additions. The relative volume fraction of Gd-123 is improved with the additions of nanosized ZnFe2O4 and CoFe2O4 up to 0.06 wt. % and 0.01 wt. %, respectively. The PIXE results show that the elemental contents are very close to the starting values. The use of the SDD detector allows the detection of Zn and Fe which was not possible by using the Si-Li detector. RBS measurements allow the exact determination of the oxygen content which is found very close to the theoretical values predicted by Rietveld’s method. The results of the measurement of electrical resistivity show that superconducting transition temperature Tc for (ZnFe2O4)xGdBa2Cu3O7-δ increases with x up to 0.06 wt.%, On the other hand Tc for Gd-123 added with ferromagnetic nanosized CoFe2O4 suppresses as x increases from 0.0 to 0.40 wt. %. The Room temperature Vickers microhardness V H was also measured and the elasticity parameters including the longitudinal modulus (L), the shear modulus (G), the bulk modulus (B), the poisson’s ratio (σ), the young’s modulus (Y) were measured and found to be higher than those of the pure sample. These parameters are corrected to zero porosity by the different models to correlate them to Hv .The proportionality constant between 0 E and v H , 0 G and v H is strongly dependent on the porosity correction as well the kind of the superconducting material and its structure. The Debye temperature θD was determined for the samples and the values of the electron-phonon coupling constant λ are less than one, indicating that the electron-phonon coupling interaction is weak. The ac magnetic susceptibility measurements were measured under different applied dc magnetic fields. The diamagnetism factor increases up to x=0.06 wt. % and x=0.01wt. % for (ZnFe2O4)xGdBa2Cu3O7-δ and (CoFe2O4)xGdBa2Cu3O7-δ, respectively. The logarithmic plot of Hirr versus (1-Tirr/T0B) shows a crossover from 3D to 2D fluctuations of the vortices at a field of 500 Oe for (ZnFe2O4)x GdBa2Cu3O7-δ samples and 1000 Oe for (CoFe2O4)x GdBa2Cu3O7-δ samples, independent of the measuring parameters. The experimental data of Hirr versus Tirr are well fitted according to Matsushita’s formula. Finally the EPR measurements reveals that the spectra are isotropic and the g value was calculated for different nanoferrites additions at different temperatures.