The interaction between elastic waves and magnetization dynamics in magnetic thin films offers a powerful route to enabling ultrafast, low-power spintronic devices. In this work, we investigate the all-optical generation of surface acoustic waves (SAWs) in the GHz range using plasmonic nanoantennas, aiming to achieve resonant magnetoelastic coupling in ultrathin magnetic systems. This approach enables us to probe and potentially drive spin waves via strain, leveraging nanoscale magnetoelastic effects.

Plasmonic nanoantennas excited by femtosecond laser pulses act as localized mechanical nanoresonators, launching SAWs across the substrate. This technique enables directional propagation and spectral tunability of hypersonic surface waves without requiring interdigital transducers or piezoelectric materials, providing a new level of integration for nanoscale devices. Previous pump-probe experiments, have demonstrated the optical generation and far-field detection of GHz SAWs using single nanoantennas patterned on dielectric substrates [1–3].

Here, we extend this platform to probe magnetoelastic interactions in Y₃Fe₅O₁₂ (YIG) thin films grown by pulsed laser deposition (PLD) on Gd₃Ga₅O₁₂ (GGG) substrates. YIG is a ferrimagnetic insulator widely used in magnonics due to its low magnetic damping and GHz-range precession frequencies. We characterized the magnetic properties of the 50 nm-thick YIG films by magnetometry, recording magnetization curves with the field applied both in-plane and out-of-plane to the film.

Gold nanoantenna arrays (80 × 80 µm²) were fabricated on the YIG surface via electron beam lithography. The antennas (primarily rods and rectangles) were designed with typical dimensions of ~130 nm (length), 90 nm (width), and 35 nm (height) to ensure plasmonic resonance near 800 nm, matching the probe laser wavelength. The array pitch was varied between 1.5 µm and 10 µm to study SAW propagation.

Pump-probe differential reflectivity measurements on individual nanoantennas revealed localized oscillations between 9 and 15 GHz, with damping times of around 600 ps and amplitudes on the order of ΔR/R ~ 10⁻⁵. Finite element simulations showed excellent agreement with the observed coherent acoustic dynamics. Additionally, time-resolved Faraday and Kerr rotation were used to monitor magnetization precession under variable optical and mechanical excitation, enabling the investigation of magnetoelastic coupling on femtosecond to nanosecond timescales.

References

[1] Della Pica, F., et al. (2016). Nano Lett. 16, 1428.

[2] Berte, R., et al. (2018). Phys. Rev. Lett. 121, 253902.

[3] Poblet, M., et al. (2021). ACS Photonics 8, 2846.