Metallic ferromagnet-based spin-wave logic with spin-orbit torque mediated amplification

• Applicant: Dr.-Ing. Martina Kiechle
• Subject Area: Experimental Condensed Matter Physics ; Communication Technology and Networks, High-Frequency Technology and Photonic Systems, Signal Processing and Machine Learning for Information Technology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 545435707

This project will realize a magnonic logic circuit through efficient spin-wave amplification in interconnected conduits made from metallic ferromagnetic thin films. With this I want to achieve a meaningful advancement in the performance of magnonic hardware, inspiring and enabling scalable high-speed spin-wave based computing architectures that are compatible with CMOS circuitry. Spin-wave amplification via the spin-Hall effect has been proposed in magnetic garnets by driving current through an adjacent large spin-Hall angle metal, whereby the generated spin current exerts a macroscopic torque in the opposite direction to the damping torque. While previous works have achieved some reduction in damping in metallic ferromagnets with this technique, there is still a lack of efficiency and understanding of the dependence on spin-wave type and wavelength. More importantly, the crucial aspect of actual amplification has remained elusive. Experimental difficulties arise from the distribution and density of electric current providing the necessary torque, as well as the inherently larger magnetic damping due to the conduction nature of ferromagnets. I am determined to work on overcoming these challenges and push the boundaries with a well-elaborated project plan: I will exploit a Cobalt-Iron alloy that was discovered in my group that has a damping parameter comparable to thin film magnetic garnets. The geometrical arrangements of spin-wave conduits will be optimized to obtain high current densities and spin-orbit torque strengths needed for successful amplification. The performance of spin wave propagation in the conduits is showcased by designing and fabricating interference-based spin-wave logic gates, that will later be combined into a full magnonic circuit. To guide spin waves around corners, local modifications of the dispersion relation are required. For this, we investigate the viability of using laser annealing to build/engineer components with Cobalt-Iron thin films and explore whether spin-wave amplification through spin-orbit torques can still be achieved after these modifications. Such a demonstration would be a significant step forward in technology readiness for spin-wave computing, enabling the realization of short-wavelength spin-wave devices and potentially replacing short-range electrical interconnects. Hereby, I will address the challenges associated with designing, laying out, and fabricating a spin-wave-based circuitry that utilizes two or more building blocks to perform spin-wave-based computation, while considering spatial constraints. Understanding the feasibility of spin-wave amplification through spin-orbit torques without thermal damage, exploring dispersion relation modification techniques, and addressing the design and fabrication challenges of spin-wave-based circuitry will provide crucial insights and pave the way for the development of efficient and practical spin-wave computing devices.

• DFG Programme: WBP Fellowship
• International Connection: USA
• Host: Dr. William Rippard