Date of Award
Master of Science
The area of spintronics has witnessed tremendous progress in the 21st century. During the 1980s and 1990s, the Giant and Tunnel Magnetoresistance effect dominated spintronics research with room-temperature ferromagnets(FM), metals, and insulators. Since then, the observation of several spin-based phenomena in heavy non-magnetic materials such as the Spin Hall Effects and the discovery of topological insulators have broadened the scope of spintronics research. Strong spin-orbit coupling (SOC) in topological insulators is expected to induce strong spin-orbit torques on proximal magnetic moments. This has motivated much recent interest in FM/TI systems with applications in spintronic memory and sensing. In this work, magnetron sputtered large-area Co/Bi2Se3 thin films were investigated with a custom-built magnetotransport setup. When current is passed predominantly through the Co layer we observe typical Co anisotropic magnetoresistance, but by promoting higher current density through the interface, we observe unidirectional magnetoresistance with a much larger change in resistance than Co alone. We also observe an unusual inverse current dependence. To test the contributions of each constituent material, Co/Ta and Cr/Bi2Se3 were prepared as controls, and similar observations were made in both materials, but not Co/Cr, suggesting that high SOC in the overlayer may be the driving force. While a proper understanding of our magnetoresistance data is not available at this point, the results broadly highlight the exciting prospects of observing novel phenomena in bilayer spintronic systems at room temperature.
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