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 Lu₂Bi₁Fe_3.4Ga_1.6O₁₂ 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.

当光波在两种不同介质之间的边界处折射时，由于光学各向异性（称为双折射），它可能会分成两条光线。另一方面，对于普通介质中的反射光波，反射角总是与根据反射定律所期望的入射角相同。在这里，我们报告观察到的反射自旋波或自旋波的双反射分裂，其中自旋波是指电子在磁性材料中自旋的波浪运动。我们在磁性石榴石Lu ₂ Bi ₁ Fe _3.4 Ga _1.6 O _12中测量了自旋波的传播通过使用时间分辨磁光显微镜，发现自旋波由于平面外磁化膜样品边缘处的反射而分裂为两个。系统测量与计算相结合揭示了双反射是由于与弹性波的杂交所致。