Advancing magnonics: from magnonic interferometry to dynamic hybrid systems
Date
2025
Authors
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Publisher
University of Delaware
Abstract
Spin waves are collective excitations of the electron spin system in magnetically ordered materials. Their quasiparticles – magnons – are considered promising candidates for wave-based information processing due to their robustness against local perturbations, low energy dissipation, and compatibility with Complementary Metal-Oxide-Semiconductor technology and device miniaturization. Controlled propagation and interference of spin waves enable the development of a wide range of magnonic devices, such as spin-wave logic gates, interferometers, directional couplers, demultiplexers, and transistors. This thesis addresses key challenges in magnonics, including the control of spin-wave propagation in extended thin films and the optimization of coherent coupling between spin waves and microwave photons. ☐ In the first part, we investigate the emission of a directional, focused spin-wave beam – referred to as a caustic spin-wave – from a nano-constricted microwave waveguide and its subsequent propagation into an unpatterned, extended thin yttrium iron garnet film. We observe non-reciprocal propagation of the beam that depends on the orientation of the external magnetic field. This non-reciprocity arises from the chiral coupling between spin waves and the microwave magnetic field localized near the constriction. The direction of beam propagation can be tuned by adjusting either the external field or the microwave frequency. ☐ The second part of this thesis explores hybrid magnonics – a quantum framework for transducing energy and information between spin systems and other platforms, including microwave photons and magnons. We report coherent coupling between incoherent (thermal) magnons in a magnetic insulator–conductor hybrid system. Specifically, thermally excited uniform modes and higher-wavevector Damon–Eshbach modes in Ni80Fe20 couple to perpendicular standing spin waves in yttrium iron garnet, facilitated by strong interfacial exchange coupling. These observations are in good agreement with spin pumping and spin rectification measurements. ☐ We further examine magnon–photon hybridization in both bulk and thin-film magnetic samples using three-dimensional microwave cavities and planar resonators. By employing larger samples, strategically placing them at positions of maximum microwave magnetic field within the resonator, and engineering the resonator geometry, we optimize the coupling strength. Under strong microwave drive, the system transitions to a nonlinear regime when Suhl’s first instability condition is satisfied, leading to linewidth broadening and a reduction in coupling strength. Notably, we demonstratefor the first time-a controlled electrical readout of the magnon–photon coupling via the inverse spin Hall effect in a superconducting circuit at cryogenic temperatures. This result marks a significant step toward electrically detecting coherent light–matter interactions at the quantum level. ☐ These findings advance condensed matter physics and magnonics in particular, by addressing key challenges in wave-based information processing. The demonstrated control of spin-wave propagation and the optimized magnon–photon coupling pave the way for compact, low-power magnonic hybrid quantum devices – such as spin-wave logic gates, sensors, tunable microwave components, and scalable quantum transducers.
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Keywords
Spin waves, Electron spin system, Quantum framework, Photon hybridization