The magnetic properties of a 15uc thick LSMO thin film on SrTiO3 (STO) substrate atT=150K was investigated using the technique of ferromagnetic resonance (FMR). The FMRmeasurement of the 15uc thick LSMO thin film at a frequency f = 9.75GHz and powerP = 0.6325mW as a function of the angle between the static magnetic field H, and theeasy direction of magnetization within the sample plane in the "in-plane" (IP) configuration displayed an FMR spectrum. This resonance spectrum shows unequal resonance field peaks. The unequal peaks in the resonance field may be attributed to the uniaxial anisotropy field which satisfies the conditions for ferromagnetic resonance. The unequal peaks in the resonance field shows a maximum and minimum with negative and positive curvature which either increases or decreases with respect to the resonance field respectively. This increase or decrease in the resonance field depends on the magnetization direction. It has been shown that for a thick 15uc LSMO thin film at T = 150K the center position and the full width half maximum (FWHM) of the resonance field were 1070.1875 Oe and 159.3125 Oe respectively.

The recovery and the relaxation behaviors of the exchange bias (HE) in a Co/Cu/FeNi/FeMnspin valve has been studied via point contact technique with high field scan rates ranging from 1050 to 13500 Oe/s. The evolution of the exchange bias with the number of field cycles(n) shows a one over the square root of (n) dependence as against ln(n) in a previous study. A recovery of the exchange bias when the field cycling is stopped has been observed and the recovery ratio (R) is found to be a function of the logarithm of the recovery time (log(t)) in agreement with previous studies. The relaxation time of the exchange bias is estimated to be 6.62, 20.85, 43.10, 109.02, and 297.24 s for 13500, 5400, 2700, 1350, and 1050 Oe/s respectively. The one over the square root of (n) dependence of HE and the log (t) dependence of R have been discussed using thermal activation model.

ABSTRACTPart IThe shear rheology of nano-clay particles when dispersed in liquid CO2 underelevated pressure using the Couette geometry is studied. A high pressure attachmentwith two different measuring systems - the double gap and Mooney systems- is used for this purpose. The clays are Laponite, Quick clay, Na-fluorohectoriteand Na-montmorillonite. The shear viscosities of the dispersions are measuredunder increasing shear rates or shear stresses. In addition an ageing test is carriedout for six days for a laponite-liquid CO2 dispersion. Inertia of the system iscompensated for by control shear stress tests.Part IIE-field induced chain formations of the nano-clay particles when dispersed in theair are recorded by a camera. A glove bag is prepared in such a way as to providea Nitrogen atmosphere and the procedure is repeated in this glove bag. In bothsituations the chain formations are observed. An attempt to measure the leakageof current within the electrode is also made by means of an operational amplifierand feedback resistor, even though the measurement of the current is uncertain.

We have presented density functional theory calculations of electronic and optical properties of ZnS, MnS, CrS, and effects of Mn and Cr impurities on electronic properties of pure ZnS using the periodic program BAND. In our calculations, we have used the generalized gradient approximation (GGA) of PW91 to approximate the exchange and correlation energies. The calculated electronic band structure results show that zinc-blende ZnS is a direct band gap material. The calculated electronic band structure and DOS results are in good agreement with previous theoretical and experimental results. Our results indicate that zinc-blende CrS shows a half-metallic behavior, while MnS shows semiconducting behavior. Mn and Cr impurity substitution for Zn result in an expansion of the ZnS crystal structure and creates bulk defect states within the band gap. Mn impurities mainly affect the deep valence bands and the shallow conduction bands of ZnS. Cr impurities mainly affect the shallow and the deep valence bands. Our results for band structure and DOS show that a half-metallic behavior is found in Cr substituted ZnS while semiconducting behavior is found in Mn substituted ZnS. Finally, the frequency dependent dielectric function was calculated to study optical properties. Our results for the dielectric function show that strong and direct absorption at the sharp peak in the spectral region around 6.05 eV is due to a high density of states at the X-point within the Brillouin zone. The calculated results showed intraband absorption in the low frequency region within the band gap, due to Mn and Cr impurity levels.

Even though in the past the photovoltaic industry was dominated by single-crystalline silicon this days multi-crystalline silicon is consider to be on of the most promising material for application in low manufacturing cost solar photovoltaic arrays, consequently it has a huge potential to dominate the single-crystalline silicon in the photovoltaic industry in the next decades. However the presence of crystal defects such as dislocation and grain boundaries in multi-crystalline solar cells hugely reducing the conversion efficiency of this material compared to single crystalline silicon solar cell. Hence realizing the widespread utilization of this material will require understanding and control of the effects of this defects on the photovoltaic cell performance. Therefor we will examine the local resistivity of a given multi-crystalline sample in a dark and how it is affected by the presence of grain boundaries and the electrical activity when we cross or with in the grain boundary or twin boundaries. We have measured the resistivity of a number of samples of multi-crystalline silicon using a multi-height four-point probe.

Semiconductor core fibres represent an emerging technology with potential applications in many areas, including photovoltaics and optical transmission. Recent advances in fibre manufacturing techniques has allowed long, continuous silicon core fibres to be produced in commercial draw towers. The effect of the molten core fibre fabrication method on the electrical properties of silicon cores from glass-clad fibres have been studied. Fibres with core diameters ranging from 60 to 300 µm were produced using a CaO interface modifier between the core and cladding. Five silicon material types with increasing phosphorus doping levels were analysed before and after the drawing process using four point probe technique, supplemented with microscopy and compositional analysis. Novel techniques for preparing and measuring fibre samples were developed, which is suitable for a range of fibre diameters. Cores produced from lightly doped materials showed a large increase in conductivity, while cores produced from a relatively highly doped material showed a small decrease in conductivity. The results suggest that the manufacturing process has introduced significant amount of impurities to the silicon core, which corresponds to additional charge carriers.