Magnonics is seen nowadays as a candidate technology for energy-efficient data processing in classical and quantum systems [1]. Wavelike nature with pronounced nonlinearity and anisotropy of dispersion relations of spin waves and their quantum mechanical counterparts magnons require advanced measurement instrumentation and methodology. Brillouin light scattering (BLS) spectroscopy and microscopy was a technique of choice for many pioneering magnonic experiments [2, 3]. However, for device miniaturization, a shift towards nanoscale spin waves is necessary. Until now, the BLS technique fell short here due to its fundamental limit in maximum detectable magnon momentum (which corresponds to the spin wave wavelength of ~0.6 μm). Previous attempts to measure nanoscale spin waves relied on nanosized apertures or other plasmonic structures made of metals to locally enhance the electromagnetic field and increase the range of the accessible k-vectors. Unfortunately, the efficiency of the plasmonic approach is severely limited by high optical losses in metallic structures, which makes it unsuitable for convenient magnon measurements. Our approach uses the advantage of reduced dissipative losses of dielectric nanoresonators [4].

We have recently shown that a simple silicon disc supporting Mie resonances can increase the magnon signal by a factor of 5 and extend the range of accessible k-vectors by an order of magnitude beyond the fundamental limit of a conventional BLS microscopy setup [5, 6]. In my talk I will give an overview of the fundamentals and applications of BLS spectroscopy and microscopy. In the second half of the talk I will show how the magnon- photon interaction can be enhanced by Mie resonators and Mie resonator arrays, and how it can be used to locally probe the dynamical properties of magnetic materials and to investigate nanoscale spin-wave devices.

[1] A. V. Chumak et al., IEEE Transactions on Magnetics 58, 1 (2022)
[2] T. Sebastian et al., Frontiers in Physics 3, 35 (2015)
[3] F. Kargar et al., Nature Photonics 15, 720 (2021)
[4] M. Caldarola et al., Nature Communications 6, 7915 (2015)
[5] O. Wojewoda et al., Communications Physics 6, 94 (2023)
[6] O. Wojewoda et al., Applied Physics Letters 122, 202405 (2023)