Acoustic wave has been widely integrated into modern electronics to enable various functions, including sensing, communication, signal filtering, etc. Conventionally, acoustic waves propagate equally forward and backward. Here, we employ a fundamentally new mechanism, magneto-rotation coupling[1], to break the symmetry of the propagation, and consequently induces an unprecedented rectification ratio to 100% at the optimized condition, in accordance with the theoretical prediction. As a unique feature of surface acoustic waves, individual lattice point undergoes a rotation motion, which changes its sign according to the wave propagation direction (see the blue and red oriented circles in figure 1(a)). More than 40 years ago, Maekawa and Tachiki developed a theoretical framework [1], proposing the coupling between the lattice rotation and the magnetization via magnetic anisotropy, namely magneto- rotation coupling. Thus, to break the symmetry of the propagation, here, we employ magneto-rotation coupling to capture the chirality of the acoustic waves in a perpendicularly anisotropic ultra-thin film Ta/CoFeB(1.6 nm)/MgO (see figure 1(b)), achieving a giant nonreciprocal acoustic wave attenuation (see figure 1(c)) with a rectification ratio up to 77% [2].

**References:**

[1] S. Maekawa and M. Tachiki, Surface acoustic attenuation due to surface spin wave in ferro and antiferromagnets, AIP Conf. Proc. 29, 542 (1976). [2] M. Xu, K. Yamamoto, J. Puebla, K. Baumgaertl, B. Rana, K. Miura, H. Takahashi, D. Grundler, S. Maekawa, and Y. Otani, Nonreciprocal surface acoustic wave propagation via magneto-rotation coupling, Vol. 6, no. 32, eabb1724 (2020).

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/404c74cc9b48109c9508f92526b2d977.jpg)
Fig. 1. (a) Schematic of the nonreciprocity mechanism. (b) Illustration of the experimental setup. (c) Attenuation ofacoustic waves, P±k, near a spin-wave resonance condition for surface acoustic wavenumbers +k and -k.

 Magneto-rotation coupling inducing nonreciprocal surface acoustic waves

*Session Chair: Mathias Weiler, Technische Universitat Kaiserslautern*

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Magneto-rotation coupling inducing nonreciprocal surface acoustic waves

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