| The spin-torque-transfer (STT) effect present in nano-magnetoresistive devices has attracted extensive interest, fueled by the advances it has provided for future Magnetoresistive Random Access Memory (MRAM) and spin-torque oscillators. In this thesis, we implement perpendicular magnetic anisotropy (PMA) into magnetoresistive devices to enhance the promises of spin-torque driven applications. For this work, we have designed two different types of magnetoresistive devices, which include magnetic tunnel junctions (MTJs) and giant magnetoresistance (GMR) spin-valves, composed of Co/Pt multilayers with PMA. The Co/Pt multilayer films are optimized in terms of growth orientation, surface roughness, and switching field distribution. To focus on obtaining highly spin-polarized current, thick Co adjacent layers have been integrated. Through fabrication and measurement of the MTJ devices, we demonstrate sharp magnetization switching between well-defined parallel and antiparallel states with reasonable tunneling magnetoresistance (TMR) ratio at room temperature. The tunneling resistance of the MTJ devices can be reduced by thinning the tunnel barrier and enhancing PMA through interfacial-oxidation To demonstrate spin-torque induced behavior, we obtained current-induced magnetization switching results from the nanofabricated pseudo-spin-valve devices. The results show that the resistance change from the spin-torque induced magnetization switching is well matched with that from the external-field induced switching. The spin-torque induced behavior is further studied by designing spin-torque oscillators containing a perpendicular polarizer. As a result, detectible out-of-plane magnetization precession is demonstrated where the precessional frequency can be tuned by spin-polarized current. |
