Modeling of magnetization dynamics and applications to spin-based logic and memory devices
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The objective of this research is to develop models to better evaluate the performance and reliability of proposed spin-based boolean devices. This research will focus on a particular spin-based logic technology called Spin-Switch Logic. There are two primary reversal mechanisms that will be considered for a full evaluation of Spin-Switch technology. Firstly, nanomagnet reversal through the use of spin-transfer torque (STT) is studied. While switching through STT has been analytically solved for the uniaxial nanomagnet case, the biaxial case has yet to be studied on a sufficient scale and will be a focus of this research. Secondly, input-output isolation is achieved through dipolar coupling; hence, the performance and reliability of this type of reversal mechanism is extensively studied. It is shown that dipolar coupling strength is not only a function of geometric and material parameters, but also of reversal speed. If the reversal of a neighboring nanomagnet is very fast, the dipolar field reduces to a constant longitudinal field and can be analytically studied. However, if the reversal of the neighboring nanomagnet is slow, new models are needed to estimate the region of reliable coupling and delay. Lastly, a focal point of this research will be on the reliability of nanomagnet states in the presence of thermal noise and new models are proposed to estimate the reliability of complex spin-based systems. Not only does the thermal noise affect the probability of magnetization state consistency, it also alters nanomagnet precession during reversal, making the delay a random variable. Hence, models are developed for evaluating the variation in reversal delay through STT for both uniaxial and biaxial cases. Ultimately, these analytic models are combined to comprehensively evaluate the performance of Spin-Switch technology and identify possible improvements to this technology. While the end result of this research will be a thorough analysis of Spin-Switch logic, the models developed during this research are applicable to a variety of spin-based logic and memory technologies.