Spin-orbitronics: Electrical control of magnets via spin-orbit interaction

Relativistic effects, having far reaching consequences for advancing our fundamental understanding of the nature, have so far mostly played an academic role in solid-state systems. For example, electrons moving in atomic orbitals close to the speed of light acquire a relativistic shift in energy via the so-called spin-orbit interaction (SOI). More recently, the ability to engineer this relativistic SOI in magnetic system, has shown potential to extend the reach of relativity into technological applications by providing an energy-efficient electrical knob to control magnetic order via torques, now referred to as the spin-orbit torques (SOT). In this dissertation, this “spin-orbitronic” control of magnets interfaced with heavy elements, which in turn possess a high SOI, is presented. Starting from a symmetry-based phenomenology, the role of reduced symmetries leading to the identification of two flavors of SOT: current-induced and voltage-induced is highlighted. Focusing first on magnetic-memory-type applications, theoretical proposal and experimental demonstration of new SOT resulting from breaking additional lateral structural symmetry is then presented, which allows for the removal of power hungry external magnetic fields for switching magnets. Subsequently, the required switching currents are reduced by nearly three orders of magnitude via demonstration of extremely efficient SOT in topological insulator-based magnets with engineered inversion asymmetry. Next, motivated by going beyond memory applications, the role of SOT to create and manipulate magnetic solitons, i.e. particle-like magnetic configurations capable of storing and transporting non-volatile information is presented. This includes: (a) experimental demonstration of a scheme for current-induced creation and manipulation of such solitons utilizing inhomogeneous SOT, (b) theoretical possibility of manipulating these solitons via more energy efficient electric-field-induced SOT. Finally, excitation of magnetization dynamics in insulating magnets, for transporting information by Joule heating free “pure spin currents”, is of particular importance for low power requirement. Consequently, an optical scheme demonstrating current-induced SOT in insulating magnets is developed, followed by a proof of principle demonstration of motion of solitons via these pure spin currents