  Monoaxial chiral magnets exhibit a chiral conical magnetic state in a
magnetic field parallel to the chiral axis. The conical spins carry the
potential for nonreciprocal transport phenomena, as they break both spatial
inversion and time reversal symmetries. Here we study the spin-dependent
transport in the chiral conical magnetic state, using the Landauer method based
on Green's functions for a one-dimensional Kondo lattice model. We show that
the system exhibits nonreciprocal spin transport, which depends on the
chirality, period, cone angle, and the polarization of the spin current. In
particular, we find the distinct cone angle dependence between the spin
textures with long and short periods. We also show that the nonreciprocity is
related with the spin states of itinerant electrons near the leads. Our results
indicate that the chiral cone acts as a spin-current diode, which can be
flexibly controlled by a magnetic field.
