Bi-reflection of spin waves

Tomosato Hioki,Eiji Saitoh,Yusuke Hashimoto

doi:10.1038/s42005-020-00455-6

Tomosato Hioki, Eiji Saitoh + Show 1 more

Open Access

https://doi.org/10.1038/s42005-020-00455-6

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Abstract

When a light wave is refracted at a boundary between two different media, it may split into two rays due to optical anisotropy, a phenomenon called birefringence. On the other hand, for a reflected light wave in an ordinary medium, the angle of reflection is always the same as the incident angle as expected from the law of reflection. Here, we report the observation of a split of reflected spin-waves, or bi-reflection of spin-waves, where a spin-wave refers to a wavy motion of electron spins in a magnetic material. We measured the spin-wave propagation in a magnetic garnet Lu2Bi1Fe3.4Ga1.6O12 by using time-resolved magneto-optical microscopy and found that the spin-wave splits in two as a result of reflection at the sample edge of an out-of-plane magnetized film. Systematic measurements combined with calculations unveiled that the bi-reflection is due to the hybridization with elastic waves.

Highlights

When a light wave is refracted at a boundary between two different media, it may split into two rays due to optical anisotropy, a phenomenon called birefringence
By using timeresolved magneto-optical (TRMO) microscopy, we demonstrated that the magneto-elastic coupling induces a split of a reflected spin wave
While k1 mode has the reflection angle same as the incident angle, k2 mode has much less reflection angle. k2 mode has a shorter wavelength compared with the incident wave and k1 mode, meaning that k2 mode is owing to extraordinary reflection of spin waves

Summary

Introduction

When a light wave is refracted at a boundary between two different media, it may split into two rays due to optical anisotropy, a phenomenon called birefringence. We measured the spin-wave propagation in a magnetic garnet Lu2Bi1Fe3.4Ga1.6O12 by using time-resolved magneto-optical microscopy and found that the spin-wave splits in two as a result of reflection at the sample edge of an out-of-plane magnetized film. As a result of the conversion, when a single-mode hybridized spin wave meets a sample edge, a reflected wave can split into two different modes: bireflection of spin waves. By using timeresolved magneto-optical (TRMO) microscopy, we demonstrated that the magneto-elastic coupling induces a split of a reflected spin wave. We measured spin-wave propagation dynamics in a ferrimagnetic garnet (Lu2Bi1Fe3.4Ga1.6O12) film This material is suitable for TRMO microscopy because it has a larger magneto-optical effect than yittrium iron garnet, one of the traditional materials for investigating spin-wave dynamics (see “Methods”)[26,27].

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