Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Spin Polarized Tunneling Spectroscopy of Intercalated Bi2sr2cacu2o8+(Izmir Institute of Technology, 2006) Özdemir, Mehtap; Özyüzer, Lütfi; Özdemir, Mehtap; Özyüzer, Lütfi; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyThere has been continuing interest in decades in heterostructure tunnel junctions that combine ferromagnetic material (F), insulator (I) and superconductor (S). This junction has been known to a good probe to analyze the physical properties of ferromagnetic and superconducting materials. In order to understand the influence of the spin injection on the c-axis tunneling characteristics of a Bi-2212 single crystal as a function of temperature and magnetic field, two sets of samples have been prepared; in one set, the surface of HgBr2 intercalated Bi-2212 crystals have been deposited with merely Au while the other set has ferromagnetic multilayer (Au/Co/Au) on top of the crystal. The micron sized mesa arrays have been patterned using photolithography and ion beam etching techniques. The surface topography and height of the mesa were investigated using atomic force microscopy. Tunneling characteristics were examined by means of the novel technique, point contact tunneling (PCT), and experiment were performed wide range of temperatures from 4.2 K to 300 K and that of magnetic field from 0 G to 2600 G. The results of spin polarized tunneling measurements compared with spin degenerate tunneling. Magnetic field dependence hysteretic I-V curves with multiple branches were examined to show the suppression of the superconductivity with spin polarized current. The distinct temperature dependence of depression in tunneling conductance near Fermi level was discussed for spin degenerate and polarized currents above Tc. The zero bias conductance and resistivity versus temperature plots were investigated to show the existence of the pseudogap in tunneling spectroscopy of investigated samples.Master Thesis Microstructural, Electrical and Mechanical Properties of Mgb2/Mg Metal Matrix Composites(Izmir Institute of Technology, 2004) Eğilmez, Mehmet; Özyüzer, Lütfi; Özyüzer, Lütfi; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyThe recent discovery of superconducting MgB2 (2001) has risen a great interest because of its relatively high Tc (39 K). Furthermore, simple crystal structure, large coherence lengths, high critical current densities (Jc) and critical fields (Bc2), promise that MgB2 will be a good material for large-scale applications based on production of superconducting wires. However, MgB2 is not a stand-alone material to produce wires because of its brittle nature. The potential of MgB2/Mg composites for producing superconducting wires, is investigated. MgB2/Mg composites were prepared using metal matrix composite fabrication technique, which is an alternative to conventional wire fabrication methods such as powder in tube. MgB2 and Mg powders were mixed at different weight fractions and uniaxially pressed in a cylindrical dye under the pressure of 0.5 GPa and 1GPa for two hours at different temperatures in the air. X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Electron Dispersive X-Ray Spectroscopy (EDX) techniques were used for phase identification and microstructural studies. D.C resistivity measurements were carried on the pellet segments of the MgB2/Mg composites in the temperature range 20-300 K. Magnetization measurements were done on the composites using a vibrating sample magnetometer to characterize the magnetic properties of the samples. The effects of pressing temperature on the mechanical properties of MgB2/Mg composites were also investigated. For this purpose, compressive mechanical testing were performed to measure elastic modulus and strength at failure values of the composites. It was found that the relative weight fractions of Mg and the pressing temperature have some considerable effect on the electrical, magnetic, microstructural and the mechanical properties of the composites.