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Micromagnetic Modeling and Analysis of Magnetic Tunnel Junctions for Spintronics Applications


Magnetic materials and nanoscale devices are remaining at the center of data storage technologies, from well-known magnetic hard drives to future spintronic devices such as magnetoresistive or racetrack memory technologies. Because of the constantly increasing demand for more storage space and performance, the focus has shifted from magnetic field-based applications to spin current-based applications. Spintronic devices are taking advantage of interactions between magnetic materials and electric currents. Spin transfer torque magnetic random access memory devices utilizing perpendicular magnetic tunnel junctions are the most promising candidates for future memory applications. This thesis discusses some of the challenges faced when studying interactions between electrical spin polarized currents and magnetic tunnel junctions for magnetic random access memory application. It starts with a short introduction to micromagnetics and the description of the main magnetic interactions. It then focuses specifically on the study of the perpendicular magnetic tunnel junction and its important properties, such as size dependence, thermal stability, critical switching current density and overall device efficiency. The next chapters are dedicated to magnetic tunnel junctions’ optimal design study, including a study of composite free-layers, surface defects and roughness effects, granularity, and parameters distributions. The study of switching probability or write error rates under non-zero temperature is also present and briefly discussed. This work also includes a separate study of novel spin transfer torque nano oscillator based on synthetic antiferromagnets. All these chapters contain the numerical results and simulations performed by using the FastMag finite element micromagnetic simulation software, developed by the members of Professor Vitaliy Lomakin’s research group. Some general ideas and details on the computational methods are also provided with the intention to help understand better the engineering and analytical aspects of the devices based on magnetic tunnel junctions.

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