  We investigate the production of spin-polarized currents in corrugated
graphene nanoribbons. Such corrugations are modeled as multiple regions with
Rashba spin-orbit interactions, where concave and convex curvatures are treated
as Rashba regions with opposite signs. Numerical examples for different
separated Rashba-zone geometries calculated within the tight-binding
approximation are provided. Remarkably, the spin-polarized current in a system
with several Rashba areas can be enhanced with respect to the case with a
single Rashba part of the same total area. The enhancement is larger for
configurations with multiple regions with the same Rashba sign. This indicates
that the increase of the spin polarization is due to the scattering of the
electrons traversing regions with and without Rashba interaction. Additionally,
we relate the appearance of the spin-polarized currents to novel symmetry
relations between the spin-dependent conductances. These symmetries turn out to
be a combination of different symmetry operations in real and spin spaces, as
those occurring in non-planar systems like carbon nanotubes. Our results show
that two-dimensional devices with Rashba spin-orbit interaction can be used as
excellent spintronic devices in an all-electrical or mechanical setup.
