Spin accumulation and Andreev reflection in a mesoscopic ferromagnetic wire

The electron transport though ferromagnetic-metal-superconducting hybrid devices is considered in the nonequilibrium Green's function formalism in the quasiclassical approximation. Attention is focused on the limit in which the exchange splitting in the ferromagnet is much larger than the superconducting energy gap. Transport properties are then governed by an interplay between spin accumulation close to the interface and Andreev reflection at the interface. We find that the resistance can be either enhanced or lowered in comparison to the normal case and can have a nonmonotonic temperature and voltage dependence. Ln the nonlinear voltage regime electron heating effects may govern the transport properties, leading to qualitative different behavior than in the absence of heating effects. Recent experimental results on the effect of the superconductor on the conductance of the ferromagnet can be understood by our results for the energy-dependent interface resistance together with effects of spin accumulation without invoking long-range pairing correlations in the ferromagnet.