Spin-accumulation-induced resistance in mesoscopic ferromagnet-superconductor junctions

We present a description of spin-polarized transport in mesoscopic ferromagnet-superconductor $(F/S)$ systems, where the transport is diffusive and the interfaces are transparent. It is shown that the spin reversal associated with Andreev reflection generates an excess spin density close to the $F/S$ interface, which leads to a spin contact resistance. Expressions for the contact resistance are given for two-terminal and four-terminal geometries. In the latter the sign depends on the relative magnetization of the ferromagnetic electrodes.