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.

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.

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.

This book focuses on an increasingly important area of materials science and technology, namely, the fabrication and properties of artificial materials where slabs of magnetized materials are sandwiched between slabs of nonmagnetized materials. It includes reviews by experts on the theory and descriptions of the various experimental techniques such as those using nuclear or electron spin probes, as well as optical, X-ray or neutron probes. It also reviews potential applications such as the giant magnetoresistance, and one specialized preparation technique, the electrodeposition. The various chapters are tutorial in nature, making the subject accessible to nonspecialists, as well as useful to researchers in the field.

Magnetic Oxides offers a cohesive up-to-date introduction to magnetism in oxides. Emphasizing the physics and chemistry of local molecular interactions essential to the magnetic design of small structures and thin films, this volume provides a detailed view of the building blocks for new magnetic oxide materials already advancing research and development of nano-scale technologies. Clearly written in a well-organized structure, readers will find a detailed description of the properties of magnetic oxides through the prism of local interactions as an alternative to collective electron concepts that are more applicable to metals and semiconductors. Researchers will find Magnetic Oxides a valuable reference.

Novel Magnetic Nanostructures: Unique Properties and Applications reviews the synthesis, design, characterization and unique properties of emerging nanostructured magnetic materials. It discusses the most promising and relevant applications, including data storage, spintronics and biomedical applications. Properties investigated include electronic, self-assembling, multifunctional, and magnetic properties, along with magnetic phenomena. Structures range from magnetic nanoclusters, nanoparticles, and nanowires, to multilayers and self-assembling nanosystems. This book provides a better understanding of the static and dynamic magnetism in new nanostructures for important applications. Provides an overview of the latest research on novel magnetic nanostructures, including molecular nanomagnets, metallacrown magnetic nanostructures, magnetic dendrimers, self-assembling magnetic structures, multifunctional nanostructures, and much more Reviews the synthesis, design, characterization and detection of useful properties in new magnetic nanostructures Highlights the most relevant applications, including spintronic, data storage and biomedical applications

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.