Magnons, or spin waves, are magnetic excitations that can carry spin information.¹ Spin waves in low-damping magnetic materials are the foundation for building magnonic devices, magnetic counterparts to traditional CMOS microelectronics.^2,3

Magnons interact with magnetic textures such as domain walls, leading to domain wall motion or attenuation of the spin waves.^4-6 These phenomena provide methods of writing and reading magnetic bits for magnonic devices. Han et al. demonstrated mutual interactions between magnons and domain walls in metallic Co/Ni multilayer films.⁷ However, large damping in the metallic film limits domain wall velocities, implying slow reading and writing speeds and high power requirements for magnonic devices. 

Bismuth-doped yttrium iron garnet (BiYIG) is an insulating ferrimagnet with one of the lowest reported damping coefficients. Its low-damping and insulating properties allow magnetic domain walls to propagate through BiYIG with high velocities and minimal energy loss,^8,9 and unlike YIG, it can be grown as a thin film with out-of-plane magnetization, enabling a high density of magnetic domains to be stabilized. Thus, this material serves as a leading candidate for magnonic device applications. 

In our study, we demonstrate interactions between magnons and domain walls in BiYIG, generating the magnons by applying a GHz signal to an overlaid antenna and observing the domain walls using magnetooptical Kerr effect microscopy (see figure below). A key result is the motion of domain walls over distances of 15 µm using a 1 ns pulse. The low damping in BiYIG means spin wave-driven domain wall motion requires orders of magnitude less energy than that reported in metallic systems. These results facilitate the development of energy efficient magnonic devices utilizing spin wave/domain wall interactions to read and store information.

To learn more, please check out our publication “Coherent magnon-induced domain wall motion in a magnetic insulator channel” in Nature Nanotechnology: https://www.nature.com/articles/s41565-023-01406-2 

References

1          Kajiwara, Y. et al. Transmission of electrical signals by spin-wave interconversion in a magnetic insulator. Nature 464, 262-266, doi:https://doi.org/10.1038/nature08876 (2010).

2          Chumak, A. V., Vasyuchka, V. I., Serga, A. A. & Hillebrands, B. Magnon spintronics. Nature Physics 11, 453, doi:10.1038/nphys3347 (2015).

3          Sheng, L., Chen, J., Wang, H. & Yu, H. Magnonics Based on Thin-Film Iron Garnets. Journal of the Physical Society of Japan 90, 081005, doi:10.7566/JPSJ.90.081005 (2021).

4          Yan, P., Wang, X. S. & Wang, X. R. All-Magnonic Spin-Transfer Torque and Domain Wall Propagation. Physical Review Letters 107, 177207, doi:10.1103/PhysRevLett.107.177207 (2011).

5          Pirro, P. et al. Experimental observation of the interaction of propagating spin waves with Néel domain walls in a Landau domain structure. Appl. Phys. Lett. 106, 232405, doi:10.1063/1.4922396 (2015).

6          Sheng, L. et al. Spin wave propagation in a ferrimagnetic thin film with perpendicular magnetic anisotropy. Applied Physics Letters 117, 232407, doi:10.1063/5.0024424 (2020).

7          Han, J., Zhang, P., Hou, J. T., Siddiqui, S. A. & Liu, L. Mutual control of coherent spin waves and magnetic domain walls in a magnonic device. Science 366, 1121-1125, doi:10.1126/science.aau2610 %J Science (2019).

8          Fakhrul, T. et al. Magneto-Optical Bi:YIG Films with High Figure of Merit for Nonreciprocal Photonics. Advanced Optical Materials 7, 1900056, doi:https://doi.org/10.1002/adom.201900056 (2019).

9          Kumar, R., Samantaray, B. & Hossain, Z. Ferromagnetic resonance studies of strain tuned Bi:YIG films. Journal of Physics: Condensed Matter 31, 435802, doi:10.1088/1361-648x/ab2e93 (2019).