Deliberate control of magnon transportation will lead to an energy-efficient technology for information transmission and processing. Y3Fe5O12(YIG), exhibiting extremely large magnon diffusion length due to the low magnetic damping constant, has been intensively investigated for decades. While most of the previous works focused on the determination of magnon diffusion length by various techniques, herein we demonstrated how to tune magnon diffusion by light excitation. We found that the diffusion length of thermal magnons is strongly dependent on light wavelength when the magnon is generated by exposing YIG directly to laser beam. The diffusion length, determined by a nonlocal geometry at room temperature, is ~30 um for the magnons produced by visible light (400-650 nm), and ~136-156 um for the laser between 808 nm and 980 nm. The diffusion distance is much longer than the reported value. In addition to thermal gradient, we found that light illumination affected the electron configuration of the Fe3+ ion in YIG. Long wavelength laser triggers a high spin to low spin state transition of the Fe3+ ions in FeO6 octahedron. This in turn causes a substantial softening of the magnon thus a dramatic increase in diffusion distance. The present work paves the way towards an efficient tuning of magnon transport behavior which is crucially important for magnon spintronics.
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