Ubiquitous smart devices and internet of things create tremendous data every day, shifting computing diagram towards data-driven. Computing and memory units in traditional computers are physically separated, which leads to huge energy cost and time delay. Novel computer architectures bring computing and memory units together for data-intensive applications. These memory units need to be fast, energy efficient, scalable and nonvolatile. This dissertation concerns innovating new types of magnetic memory or spintronic devices to achieve ultrahigh energy efficiency and ultracompact size from a perspective of material and heterostructure design. Especially, we employ quantum materials to enable potentially unprecedented technological advances. The highest energy efficiency of magnetic memory requires the largest charge-to-spin conversion efficiency that allows the minimum power to manipulate the magnetization. We utilize topological surface states of topological insulators (TIs), which have unique spin-momentum locking and thus are highly spin-polarized. We discover giant spin-orbit torques (SOTs) from TIs at room temperature, which are more than one order of magnitude larger than those of traditional heavy metals. We integrate TIs into room temperature magnetic memories, which promises future ultralow power dissipation. SOT characterization methods and related SOT studies on heavy metals, monolayer two-dimensional materials, and magnetic insulators-based heterostructures are discussed in detail. To have the best scaling performance, we investigate emerging topological skyrmions in magnetic thin films, which are arguably the smallest spin texture in nature. While most of the skyrmions are discovered in metallic systems, insulating skyrmions are desired thanks to their lower damping and thus potentially lower power dissipation. We observe high-temperature electronic signatures of skyrmions in magnetic insulators, topological Hall effect, by engineering heterostructures consisting of heavy metals and magnetic insulators. This new platform is essential for exploring fundamental magnon-skyrmion physics and pursuing practical applications based on insulating skyrmions. To have the highest operation speed, we explore compensated ferrimagnetic insulators, which have THz dynamics due to the strong exchange coupling field. We realize energy efficient switching of the ferrimagnetic insulator in both ferrimagnetic and antiferromagnetic states, promising electrical manipulation of ultrafast dynamics.

Since the dawn of Big Data, the exponentially increasing demands for larger data volumes and higher information processing speeds have given the field of spintronics an astonishing momentum. In spintronics, the electron spins and their associated magnetic moments interplay with electronic charges, lattices, and even photons. These diverse interactions open endless possibilities for a new generation of fast, efficient, and non-volatile memory and logic devices to serve and fuel Big Data. Lying at the heart of innovating spintronic memory and logic devices is the search for advanced materials and mechanisms to control spin and magnetism.Following this line of research, this dissertation focuses on exploring two emerging material classes, namely, topological insulators and ferrimagnets, which hold great promise for efficient and fast magnetization manipulation. More specifically, topological insulators exhibit an extraordinary charge-spin conversion efficiency owing to their exotic surface states and can be employed to manipulate magnetic moments with minimal energy. Ferrimagnets, by contrast, are of technical interest for fast magnetization manipulation because their two non-equivalent and antiparallel aligned sublattices uniquely combine the antiferromagnet-like ultrafast dynamics with the ferromagnet-like readability/controllability for well-established techniques. However, these novel materials have been difficult to investigate using conventional magnetometers or magnetic resonance techniques. To address these challenges, an experimental platform integrating a magneto-optical Kerr effect magnetometer, a femtosecond optical pump-probe technique, and common magneto-transport measurements, was first established. Using this experimental platform, the charge-spin conversion efficiency was investigated and accurately quantified for a topological insulator-based magnetic bilayer, and a critical role of the topological surface states with spin-momentum locking was unveiled. With innovative material engineering, topological insulators were integrated with widely used metallic ferromagnet in a topological insulator/Mo/CoFeB/MgO structure. This topological insulator/Mo/CoFeB/MgO structure demonstrates high thermal stability, robust magnetic properties, and efficient magnetization switching driven by spin-orbit torques. The systematically calibrated efficiency confirms that, for a room temperature magnetic memory, topological insulators are at least one order of magnitude more efficient than conventional heavy metals. Moreover, the annealing effects were carefully studied in this structure, and desirable thermal compatibility with modern CMOS technology has also been achieved, empowering the development of advanced spintronic applications. To realize faster control of magnetic moments, the dynamical characteristics of a compensated ferrimagnetic GdFeCo film with a vertical compositional gradient were investigated through the laser-induced ultrafast spin dynamics. It is found that the vertical composition gradient significantly alters the ultrafast spin dynamics. Surprisingly, these distinct spin dynamics can be handily controlled by tuning the power of laser excitation, indicating the existence of more efficient energy pathways to control magnetization with high speed. These observations motivate ferrimagnets with a composition gradient as an ideal candidate for efficient and fast magnetization manipulation. Emboldened by the findings in this dissertation, topological insulators and ferrimagnets undoubtedly possess a vast potential in increasing the efficiency and speed of magnetization manipulation for advancing spintronic memory and logic devices.

This book presents both experimental and theoretical aspects of topology in magnetism. It first discusses how the topology in real space is relevant for a variety of magnetic spin structures, including domain walls, vortices, skyrmions, and dynamic excitations, and then focuses on the phenomena that are driven by distinct topology in reciprocal momentum space, such as anomalous and spin Hall effects, topological insulators, and Weyl semimetals. Lastly, it examines how topology influences dynamic phenomena and excitations (such as spin waves, magnons, localized dynamic solitons, and Majorana fermions). The book also shows how these developments promise to lead the transformative revolution of information technology.

In a new branch of physics and technology, called spin-electronics or spintronics, the flow of electrical charge (usual current) as well as the flow of electron spin, the so-called "spin current", are manipulated and controlled together. This book is intended to provide an introduction and guide to the new physics and applications of spin current.

Handbook of Magnetic Materials, Volume 29, highlights new advances in the field, with this new volume presenting interesting chapters written by an international board of authors on topics such as spin-orbit torque. Provides the authority and expertise of leading contributors from an international board of authors Presents the latest release in the Handbook of Magnetic Materials series

STAY UP TO DATE ON THE STATE OF MRAM TECHNOLOGY AND ITS APPLICATIONS WITH THIS COMPREHENSIVE RESOURCE Magnetic Memory Technology: Spin-Transfer-Torque MRAM and Beyond delivers a combination of foundational and advanced treatments of the subjects necessary for students and professionals to fully understand MRAM and other non-volatile memories, like PCM, and ReRAM. The authors offer readers a thorough introduction to the fundamentals of magnetism and electron spin, as well as a comprehensive analysis of the physics of magnetic tunnel junction (MTJ) devices as it relates to memory applications. This book explores MRAM's unique ability to provide memory without requiring the atoms inside the device to move when switching states. The resulting power savings and reliability are what give MRAM its extraordinary potential. The authors describe the current state of academic research in MRAM technology, which focuses on the reduction of the amount of energy needed to reorient magnetization. Among other topics, readers will benefit from the book's discussions of: An introduction to basic electromagnetism, including the fundamentals of magnetic force and other concepts An thorough description of magnetism and magnetic materials, including the classification and properties of magnetic thin film properties and their material preparation and characterization A comprehensive description of Giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR) devices and their equivalent electrical model Spin current and spin dynamics, including the properties of spin current, the Ordinary Hall Effect, the Anomalous Hall Effect, and the spin Hall effect Different categories of magnetic random-access memory, including field-write mode MRAM, Spin-Torque-Transfer (STT) MRAM, Spin-Orbit Torque (SOT) MRAM, and others Perfect for senior undergraduate and graduate students studying electrical engineering, similar programs, or courses on topics like spintronics, Magnetic Memory Technology: Spin-Transfer-Torque MRAM and Beyond also belongs on the bookshelves of engineers and other professionals involved in the design, development, and manufacture of MRAM technologies.

This book discusses theoretical and experimental advances in metamaterial structures, which are of fundamental importance to many applications in microwave and optical-wave physics and materials science. Metamaterial structures exhibit time-reversal and space-inversion symmetry breaking due to the effects of magnetism and chirality. The book addresses the characteristic properties of various symmetry breaking processes by studying field-matter interaction with use of conventional electromagnetic waves and novel types of engineered fields: twisted-photon fields, toroidal fields, and magnetoelectric fields. In a system with a combined effect of simultaneous breaking of space and time inversion symmetries, one observes the magnetochiral effect. Another similar phenomenon featuring space-time inversion symmetries is related to use of magnetoelectric materials. Cross-coupling of the electric and magnetic components in these material structures, leading to the appearance of new magnetic modes with an electric excitation channel – electromagnons and skyrmions – has resulted in a wealth of strong optical effects such as directional dichroism, magnetochiral dichroism, and rotatory power of the fields. This book contains multifaceted contributions from international leading experts and covers the essential aspects of symmetry-breaking effects, including theory, modeling and design, proven and potential applications in practical devices, fabrication, characterization and measurement. It is ideally suited as an introduction and basic reference work for researchers and graduate students entering this field.