Spin Current Generation in Magnetic Heterostructures and its Impact on Terahertz Emission : A Spin Dynamics Perspective

Abstract: The transfer of knowledge from one generation to another is key to the intellectualness of mankind. In the present information age, digital technology provides easy access to knowledge and information. However people across the globe simultaneously generate an enormous digital footprint, which demands to store and process the information in a modish way. Spin-based electronics is being considered a prospective candidate beyond complementary metal-oxide-semiconductor technology with several applications in data storage and data communication. The key concept of this technology is the generation, transportation, and detection of spin currents in magnetic heterostructures consisting of ferromagnetic (FM) and non-ferromagnetic (NFM) bilayer thin films.In this thesis, I describe the concepts of spin dynamics at the nano- to femtosecond timescales and experimental techniques used to extract the spin dynamics properties of magnetic heterostructures. In this regard, we have shown that the Gilbert damping parameter and the number of quantum conductance channels (QCCs) can be enhanced by doping the FM layer with Re in the Ru/Fe65Co35/Ru heterostructure. The same heterostructure was used to evidence superdiffusive spin transport and a proximity induced magnetic moment in the Ru layer. It has also been shown that the number of QCCs can be enhanced by inserting a Cu layer at the interface between the FM and NFM layers in the Co2FeAl/β-Ta heterostructure where the Gilbert damping parameter of Co2FeAl depends on its chemical ordering. Further, we have found that the spin torque (SOT) efficiency in the 2D-transition metal dichalcogenide, 1T-TaS2, based heterostructure is one order larger as compared to Co2FeAl/β-Ta and Fe/Pd heterostructures. Moreover, it has been shown that crystalline quality and strain engineering can significantly impact the SOT efficiency and emission of terahertz radiation in Fe/Pd and Fe/Pt heterostructures, respectively. Finally, a full Heusler (Co2FeAl) based spintronic terahertz emitter is presented, which utilizes an optically induced spin current and the inverse spin Hall effect phenomenon. This thesis provides useful insights in the pathway towards power efficient spin logic devices.