Propagation, manipulation and detection of magnonic spin currents in magnetic oxides and metals
Date issued
Authors
Editors
Journal Title
Journal ISSN
Volume Title
Publisher
License
Abstract
In anticipation of faster and more energy-efficient information technology, the research field of magnon spintronics aims to interface established electronics or spintronics systems with spin wave (magnon) based computing. In this thesis, aspects of magnon spintronics are investigated on a basic science level to obtain a better understanding of spin transport and detection mechanisms in different types of materials. On the more applied side, concepts of active magnon propagation and detection manipulation as a basis for magnon logic operations are explored.
As an essential prerequisite for magnon spintronics devices, spin information exchange via magnonic spin currents is investigated in a ferrimagnetic insulator, revealing a complex interplay of multiple competing mechanisms. In a non-local transport experiment that allows one to examine both thermally (spin Seebeck effect) and electrically (spin Hall effect) induced spin currents, it is shown that the thermal signal changes sign as a function of distance and temperature, which is partly attributable to the de-localized generation of magnons. Additionally, the spin transport mechanism in a metallic antiferromagnet is probed following an increased interest in these materials due to advantages like enhanced stability compared to ferromagnets. Performing a spin transmission experiment, a strong reduction of the spin signal is observed when long-range antiferromagnetic order is established. This effect can be explained by the opening of an antiferromagnetic magnon gap, revealing notable magnonic spin transport in the material.
Since magnon spintronics aims to integrate electronics and magnonics, the efficient generation and detection of magnons by charge signals requires materials that exhibit large spin-charge interconversion. To this end, a binary alloy is developed and the spin Hall effect is studied as a function of the composition. By means of spin current injection, the alloy structure with the maximal spin Hall angle is identified. Furthermore, DC and THz spin current stimuli yield comparable results, demonstrating that existing magnon spintronics concepts can be readily transferred into the ultrafast regime.
Regarding magnon logic, the active manipulation of magnon detection is explored in different multilayer systems that include a metallic ferromagnet serving as a spin current detector. In both spin pumping and non-local transport measurements a spin valve-like effect with an amplitude of up to 120% can be implemented, which can be used as a switch component. Finally, the impact of actively manipulating the magnon propagation in a ferrimagnetic insulator is investigated, showing an influence of Joule heating in addition to a significant signal modulation due to applied Oersted fields.
Altogether, the results and findings presented in this thesis contribute to the key requirements for the development of magnon spintronics. The complexities of magnon propagation and detection processes are revealed and new information processing schemes are suggested, pointing towards new routes in this interesting field of research.