Spin-orbit Torques in Magnetic Heterostructures

Abstract

In the rapidly evolving landscape of modern electronics, where the relentless pursuit of enhanced performance and miniaturization has driven technological advancements, Moore's law has served as a guiding principle. However, as this law approaches a state of saturation due to the constant miniaturization of electronic components, alternative pathways, particularly spintronics, are being explored. This dissertation focuses on spin-orbit torque (SOT) as a key mechanism within spintronics to sustain and extend Moore's law. The study investigates the SOT-induced magnetization reversal in ferromagnetic layers with both in-plane magnetic anisotropy (IMA) and perpendicular magnetic anisotropy (PMA). By characterizing SOT-induced effective fields in these heterostructures, the research demonstrates the capability to switch magnetization orientation. Taking a comprehensive approach, the investigation merges fundamental principles with practical applications, employing a heavy metal/ferromagnetic/heavy metal (HM/FM/HM) model for SOT devices. The thesis unfolds with an introductory background on spin-orbit coupling and its effects on magnetic heterostructures, followed by a detailed description of experimental techniques and the room temperature transport measurements setup. Subsequent chapters delve into the separation of spin-orbit torque components from thermoelectric effects, the detection of SOT induced field-free magnetization switching, exploration of multistate memory behavior, and the detection of in-plane magnetization switching using the odd symmetry planar Hall effect. The study introduces novel reading mechanisms, such as the anomalous Nernst effect (ANE) and odd planar Hall voltage (O-PHV), to deepen understanding and demonstrate the potential of SOT-induced magnetization switching in various devices. The research reveals multistate memory behavior with potential applications in neuromorphic computing. The thesis concludes by summarizing key findings, and paving the way for future investigations in the field of spintronics, with a specific emphasis on spin-orbit torque.