  We report experimental observation of the refraction and re ection of
propagating magnetostatic spin waves crossing a 90-degree domain wall (DW) in
terms of time-resolved magneto-optical imaging. Due to the magnetization
rotation across the 90-degree DW, the dispersion relation of magnetostatic spin
waves rotates by 90 degrees, which results in the change in the propagation
dynamics of spin waves in both sides of the DW. We observe the refraction and
re ection of magnetosatatc spin waves at the 90-degree DW, and reveal their
characteristics, such as negative refraction. The incident-angle dependence of
the refraction angle is explained by the wavenumber conservation along the DW,
same as the case of Snell's law for light.
