Spin Transport and Dynamics in Spintronic Devices Based on Novel Materials

Abstract

Current computing technologies based on the von Neumann architecture suffer fromthe so-called memory wall; a performance limitation in large-scale data computation attributed to the highly energy-inefficient transfer of information between physically separated processing and memory units. With the burgeoning of big data, artificial intelligent applications, and the emergence of the metaverse, the implementation of a new computing paradigm that eliminates the memory wall is highly desirable. Magnetic random-access memory (MRAM) devices are envisioned to enable unprecedented technological advances through the implementation of the so-called in-memory computing, a novel computing paradigm that promotes the memory to an active role, eliminating the memory wall. Notwithstanding, remaining issues related to the performance of such devices, such as those related to energy-efficiency, prevent their immediate and full implementation into memory-centric computing. Hence, out-of-the-box rethinking of MRAM design and working principles is required for their successful implementation in next-generation technologies. The focus of the present thesis is to demonstrate the potential of newly discovered quantum materials and unique spin-related nanoscale phenomenon for applications in magnetic-based in-memory computing technologies. A new working principle that results in giant tunneling magnetoresistance ratios in magnetic tunnel junctions (MTJs) composed of magnetic Weyl semimetals (MWSs), a newly discovered class of magnetic topological materials, is proposed; the interplay between electron chirality and magnetization in MWSs gives rise to a mechanism to controllably suppress tunneling currents in tunneling junctions. Further, it is shown that the unique spin texture of Fermi arc states at the interface of a MWS with an insulator leads to a giant spin torque in MTJs comprising one MWS electrode, which might favor efficient current-induced magnetization switching in these systems. Next, we propose that the valley degree of freedom in two-dimensional transition metal dichalcogenides can be utilized to induce a sizable spin torque on the magnetization of an overlaid ferromagnetic thin film. The mechanism involves the generation of a local non-equilibrium spin density accumulation due to valley Hall effect and the subsequent tunneling of spin polarized carriers into a CoFe or Fe layer. Finally, a systematic study of the simultaneous impact of conventional and unconventional spin-orbit torques on the dynamics of a perpendicular magnetization in ferromagnetic/non-magnetic bilayers is presented. The presence of unconventional spin-orbit torques is shown to have a great impact on the state diagram of the perpendicular magnetization and might enable highly energy-efficient switching with several order of magnitude benefit. The proposals presented in body of this thesis offer unique qualitative and quantitative predictions related to the optimization of spin-related effects at nanoscale, which might open up opportunities towards the development of next-generation magnetic memory technologies.