Optical control of spin waves in hybrid magnonic-plasmonic structures

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School of Science | Doctoral thesis (article-based) | Defence date: 2025-11-13
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Date

2025

Department

Teknillisen fysiikan laitos
Department of Applied Physics

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Mcode

Degree programme

Language

en

Pages

155 + app. 65

Series

Aalto University publication series Doctoral Theses, 224/2025

Abstract

The advent of artificial intelligence, alongside advancements in next-generation communication technologies and brain-inspired computing, has vaulted wave‑based information processing into the spotlight of both fundamental and applied research. By encoding data in wave parameters, these systems offer an energy-efficient alternative to traditional charge-based electronics, while providing inherent parallelism. Magnonics meets these demands by harnessing spin waves and their chargeneutral quanta, magnons, enabling fast, low-power data processing across a broad frequency spectrum, from the GHz to THz range, with rich nonlinear dynamics and potential for scalable onchip integration. However, effective information encoding in magnonic systems critically depends on precise spatial and temporal control of spin-wave propagation. To address this challenge, this thesis investigates rapid optical manipulation of spin-wave transport in hybrid magnonic–plasmonic structures. By integrating gold nanodisk arrays on top of low-damping yttrium iron garnet films, this work intentionally tailors the excitation of collective surface lattice resonances to enhance light absorption and induce localized thermoplasmonic effects. The thesis presents three main contributions: (1) optical control of spin waves using localized plasmonic heating, (2) dynamic magnonic crystals enabled by spatiotemporal plasmon excitation, and (3) spin-wave transmission and mode conversion in microscopic yttrium iron garnet waveguides with embedded magnonic crystals. In the first part, a direct correlation between plasmonic light absorption and spin-wave suppression is experimentally demonstrated and supported by thermal modeling combined with micromagnetic simulations. Through thermoplasmonic heating via the surface lattice resonance mode, laser pulses of just a few hundred nanoseconds suppress spinwave signals by up to 20 dB. The underlying mechanism is attributed to a reduction in magnetization beneath the plasmonic array. The second part extends this concept by patterning one-dimensional plasmonic stripe arrays on yttrium iron garnet films. Short laser pulses (100–500 ns) induce periodic magnetization modulations, creating reconfigurable magnonic band structures. Time-resolved propagating spin-wave spectroscopy reveals the emergence of multiple bandgaps and minibands due to Bragg scattering. These band structures can be tuned by adjusting the stripe geometry or laser parameters. Finally, spin-wave propagation is studied in waveguides of various geometries, with integrated magnonic crystal regions. Using super-Nyquist sampling magneto-optical Kerr effect microscopy, the experiments reveal symmetric and asymmetric interference patterns, spin-wave self-focusing, and interconversion between quantized width modes. These results establish thermoplasmonics as a powerful tool for precise, on-demand control of spinwave propagation on micrometer scales and submicrosecond timescales. By bridging the fields of magnonics and plasmonics, this thesis lays the groundwork for the development of multifunctional hybrid magnonic devices with tunable and reconfigurable functionalities.

Description

Supervising professor

van Dijken, Sebastiaan, Prof., Aalto University, Department of Applied Physics, Finland

Thesis advisor

Qin, Huajun, Prof., Wuhan University, China

Keywords

magnetism, magnonics, plasmonics, hybrid magnonic-plasmonic structures, spin waves, optical control of spin waves, surface lattice resonance, thermoplasmonic heating

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Parts

  • [Publication 1]: Nikolai Kuznetsov, Huajun Qin, Lukáš Flajšman, Sebastiaan van Dijken. Tuning of spin-wave transmission and mode conversion in microscopic YIG waveguides with magnonic crystals. Journal of Applied Physics, 132, 193904, November 2022.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202301181171
    DOI: 10.1063/5.0123234 View at publisher
  • [Publication 2]: Nikolai Kuznetsov, Huajun Qin, Lukáš Flajšman, Sebastiaan van Dijken. Optical control of spin waves in hybrid magnonic-plasmonic structures. Science Advances, 11, eads2420, January 2025.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202501171268
    DOI: 10.1126/sciadv.ads2420 View at publisher
  • [Publication 3]: Nikolai Kuznetsov, Huajun Qin, Lukáš Flajšman and Sebastiaan van Dijken. Dynamic magnonic crystals based on spatiotemporal plasmon excitation. Advanced Materials, 2502474, June 2025.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202509037100
    DOI: 10.1002/adma.202502474 View at publisher

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Permanent link to this item

https://urn.fi/URN:ISBN:978-952-64-2820-8

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[diss] Perustieteiden korkeakoulu / SCI