Nonreciprocity in magnon-Phonon coupling

Context of project
Nonreciprocity is a phenomenon that has intrigued scientists and technologist for decades. In terms of technology, it has made tremendous impact, one particular and common example is the electronic diode (rectifier). In terms of scientific research it is usually a wonder the microscopic origins of such nonreciprocal phenomena. In this project, we explore the nonreciprocity mechanism when surface acoustic waves are absorbed by a thin ferromagnetic layer in resonance conditions, when spin waves are excited. 
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Abstract of our recent work
A fundamental form of magnon-phonon interaction is an intrinsic property of magnetic materials, the “magnetoelastic coupling.” This form of interaction has been the basis for describing magnetostrictive materials and their applications, where strain induces changes of internal magnetic fields. Different from the magnetoelastic coupling, more than 40 years ago, it was proposed that surface acoustic waves may induce surface magnons via rotational motion of the lattice in anisotropic magnets. However, a signature of this magnon-phonon coupling mechanism, termed magneto-rotation coupling, has been elusive. Here, we report the first observation and theoretical framework of the magneto-rotation coupling in a perpendicularly anisotropic film Ta/CoFeB(1.6 nanometers)/MgO, which consequently induces nonreciprocal acoustic wave attenuation with an unprecedented ratio of up to 100% rectification at a theoretically predicted optimized condition. Our work not only experimentally demonstrates a fundamentally new path for investigating magnon-phonon coupling but also justifies the feasibility of the magneto-rotation coupling application.

Read more
Nonreciprocal surface acoustic wave propagation via magneto-rotation coupling
M. Xu, K. Yamamoto, J. Puebla, K. Baumgaertl, B. Rana, K. Miura, H. Takahashi, D. Grundler, S. Maekawa, Y. Otani
Science Advances 6 (32), eabb1724 (2020)
advances.sciencemag.org/content/6/32/eabb1724

Recent theoretical work of the inverse effect: 
Non-reciprocal Pumping of Surface Acoustic Waves by Spin Wave Resonance
K Yamamoto, W Yu, T Yu, J Puebla, M Xu, S Maekawa, G Bauer
Journal of the Physical Society of Japan 89 (11), 113702 (2020)
journals.jps.jp/doi/full/10.7566/JPSJ.89.113702