  We study the spin-dependent magneto conductance in mesoscopic rings subject
to an inhomogeneous in-plane magnetic field. We show that the polarization
direction of transmitted spin-polarized electrons can be controlled via an
additional magnetic flux such that spin flips are induced at half a flux
quantum. This quantum interference effect is independent of the strength of the
nonuniform field applied. We give an analytical explanation for one-dimensional
rings and numerical results for corresponding ballistic microstructures.
