Spin filter effects in mesoscopic ring structures

We study the spin-dependent conductance of ballistic mesoscopic ring systems in the presence of an inhomogeneous magnetic field. We show that, for the set-up proposed, even a small Zeeman splitting can lead to a considerable spin polarization of the current. Making use of a spin-switch effect (Frustaglia et al2001 Phys. Rev. Lett. 87 256602) we propose a device of two rings connected in series that in principle allows for both creating and coherently controlling spin polarized currents at low temperatures