  It is a well-established notion that the spin of a magnon should be flipped
when it passes through a $180^{\circ}$ domain wall (DW) in both ferromagnets
and antiferromagnets, while the magnon spin transport through ferrimagnetic DW
is still elusive. In this work, we report that the magnon preserves its spin
after the transmission through an atomically sharp DW in ferrimagnets, due to
the intriguing interband magnon scattering at the domain interface. This
finding may provide significant insight to resolve the puzzling insensitivity
of magnon spin diffusion to the $180^{\circ}$ ferrimagnetic DWs observed by
recent experiments. Our results reveal the unique role of ferrimagnetic DWs in
manipulating the magnon spin and may facilitate the design of novel magnonic
devices based on ferrimagnets.
