  Spin waves are collective excitations propagating in the magnetic medium with
ordered magnetizations. Magnonics, utilizing the spin wave (magnon) as
information carrier, is a promising candidate for low-dissipation computation
and communication technologies. We discover that, due to the
Dzyaloshinskii-Moriya interaction, the scattering behavior of spin wave at a
magnetic domain wall follows a generalized Snell's law, where two magnetic
domains work as two different mediums. Similar to optical total reflection that
occurs at the water-air interfaces, spin waves may experience total reflection
at magnetic domain walls when their incident angle larger than a critical
value. We design a spin wave fiber using a magnetic domain structure with two
domain walls, and demonstrate that such a spin wave fiber can transmit spin
waves over long distance by total internal reflections, in analogy to an
optical fiber. Our design of spin wave fiber opens up new possibilities in pure
magnetic information processing.
