Public defence in Engineering Physics, M.Sc. Nikolai Kuznetsov

Title of the thesis: Optical Control of Spin Waves in Hybrid Magnonic-Plasmonic Structures

Thesis defender: Nikolai Kuznetsov
Opponent: Professor Dirk Grundler, Institute of Materials and Institute of Microengineering (EPFL), Switzerland
Custos: Professor Sebastiaan van Dijken Aalto University School of Science

Modern technologies such as artificial intelligence and high-speed communications demand faster and more energy-efficient ways to handle data. One promising solution is wave-based computing, where information is carried by waves instead of electric charges. This doctoral research focuses on magnonics, which utilizes magnons, the quanta of spin waves, to transfer and process information across a wide frequency range from GHz to THz without energy losses due to Joule heating. Effective data encoding in such systems requires precise control of spin waves in space and time. This thesis explores how light-induced excitation of collective plasmon resonances and the resulting thermoplasmonic effects can be used to manipulate spin waves in hybrid magnonic–plasmonic structures, offering the potential for fast, high-resolution control.

The main results show that thermoplasmonic heating in magnetic thin films integrated with gold nanodisk arrays can suppress spin-wave signals by up to 20 dB using single laser pulses lasting just a few hundred nanoseconds. Experiments and micromagnetic simulations reveal a strong correlation between plasmonic light absorption and spin-wave control. Additionally, the study demonstrates the realization of dynamic magnonic crystals by integrating one-dimensional periodic plasmonic stripe arrays on magnetic films. These hybrid structures enable formation of tunable magnonic bandgaps, providing a new approach for precise, reconfigurable control of spin waves.

These findings establish thermoplasmonics as a powerful tool for on-demand control of spin-wave propagation on micrometer scales and submicrosecond timescales. By bridging magnonics and plasmonics, this research lays the foundation for multifunctional hybrid devices with tunable and reconfigurable functionalities, offering substantial potential for applications in wave-based information processing.

Keywords: Magnetism, Magnonics, Plasmonics, Hybrid magnonic-plasmonic structures, Spin waves, Optical control of spin waves, Surface lattice resonance, Thermoplasmonic heating

Contact information: nikolai.1.kuznetsov@aalto.fi 

Thesis available for public display 7 days prior to the defence at Aaltodoc.