Abstract: Recent advances in generating, manipulating and detecting spin-polarized electrons have stimulated great interest in new types of devices called spintronic devices. The key component of many spintronic devices is the magnetic tunnel junction (MTJ), which consists of a sandwich of two layers of ferromagnetic (FM) electrodes separated by a tunneling barrier. These structures display two resistance states for parallel (low resistance) and anti-parallel (high resistance) orientation of the FM layers and this change in resistance is termed tunneling magnetoresistance (TMR). In this dissertation, various microstructural aspects of these magnetic multilayer structures have been studied. The magnetization in one of the FM electrodes in an MTJ is usually pinned using an antiferromagnetic (AFM) layer by a phenomenon called exchange bias. FM/AFM bilayers of Cobalt/Cobalt-Magnesium-Oxide (Co/CoMgO) with Co grown above and below the AFM layer were investigated for their exchange bias behavior. Enhancement of exchange bias field was obtained by dilution of AFM Coo with Mg and this enhancement was explained by the interfacial uncompensated spin density model. MTJs with a barrier layer of semi-conducting Chromium(2)-Oxygen(3) were investigated for their TMR behavior. Very low TMR obtained from these MTJs was attributed to the incomplete oxidation of the barrier and partial oxidation of the FM layer underneath. MTJ structures with polycrystalline MgO barrier and top electrode of Aluminum (Al) were studied for the optimization of Al thicknesses for spin-polarization measurements. It was found that Al electrodes of different optimum thicknesses were required for samples annealed at different temperatures, which was attributed to oxidation of the Al top surface. MTJs with FM Chromium dioxide as one electrode and other Nickel-Oxide/Magnesium-Oxide (NiO/MgO) double-barrier MTJs were found to display negative TMR. Electron microscopy results indicated the presence of AFM oxide at the FM-barrier interface as a possible source for the observed negative TMR.