  Introducing noncollinear magnetization into a monolayer CrI$_3$ is proposed
to be an effective approach to modulate the local electronic properties of the
two-dimensional (2D) magnetic material. Using first-principles calculation, we
illustrate that both the conduction and valence bands in the monolayer CrI$_3$
are lowered down by spin spiral states. The distinct electronic structure of
the monolayer noncollinear CrI$_3$ can be applied in nanoscale functional
devices. As a proof of concept, we show that a magnetic domain wall can form a
one-dimensional conducting channel in the 2D semiconductor via proper gating.
Other possible applications such as electron-hole separation and identical
quantum dots are also discussed.
