Hybridization of Spin Waves and Surface Acoustic Waves

Speaker: Jorge Puebla

Department of Electronic Science and Engineering, Kyoto University, Japan and Center for Emergent Matter Science, RIKEN, Wako-shi, Saitama, Japan https://jorgepuebla.weebly.com/

Abstract:  The interaction between surface acoustic waves (SAWs) and spin waves is attracting growing interest in spintronics and magnetism [1]. While spin waves in ferromagnets are typically excited by microwave photons, they can also be driven by phonons, as predicted by Kittel [2]. When SAWs and spin waves strongly couple, hybrid quasiparticles emerge, blending phononic and magnonic characteristics. Our recent experiments demonstrate such hybridization at room temperature in an on-chip SAW device [3]. Using acoustic reflectors to form a low-loss cavity [4, 5] and CoFeB layers with low damping, we observed avoided crossing in the dispersion curves, a hallmark of strong coupling. SAW transmission data revealed bending in the phonon dispersion near magnon resonance. With a 10 nm CoFeB layer, energy absorption at ~30 mT was evident, but the dispersion remained linear. At 20 nm, both absorption and bending occurred, confirming strong coupling. This indicates that phonons acquire magnon-like properties and respond to magnetic fields, and vice versa, opening paths for hybrid-wave-based information and communication devices. Furthermore, in the thin-film regime where the acoustic wavelength exceeds the magnetic layer thickness, we observed a monotonic increase in coupling strength with CoFeB thickness, suggesting a pathway toward ultra-strong coupling. In this talk, I will present these findings and discuss their potential impact on future hybrid magnon-phonon devices, especially as improved experimental techniques enable deeper insight into their spatial, temporal, and phase dynamics. 

References:[1] J. Puebla, Y. Hwang, S. Maekawa, Y. Otani, Perspectives on spintronics with surface acoustic waves, Appl. Phys. Lett. 120, 220502 (2022) 

[2] C. Kittel, Interaction of Spin Waves and Ultrasonic Waves in Ferromagnetic Crystals, Phys. Rev. 110, 836 (1958) 

[3] Y. Hwang, J. Puebla, K. Kondou, C. Gonzalez-Ballestero, H. Isshiki, C. Sanchez Munoz, L. Liao, F. Chen, W. Luo, S. Maekawa and Y. Otani, Strongly Coupled Spin Waves and Surface Acoustic Waves at Room Temperature, Phys. Rev. Lett. 132, 056704 (2024)

 [4] Y. Hwang, J. Puebla, M. Xu, A. Lagarrigue, K. Kondou, Y. Otani, Enhancement of acoustic spin pumping by acoustic distributed Bragg reflector cavity, Applied Physics Letters 116, 252404 (2020) 

[5] D. Hatanaka, M. Asano, H. Okamoto, Y. Kunihashi, H. Sanada, and H. Yamaguchi, On-Chip Coherent Transduction between Magnons and Acoustic Phonons in Cavity Magnomechanics, Phys. Rev. Applied 17, 034024 (2022)

Seminar, which will be held ONLINE (as an exceptional arrangement)