Charge and spin diffusion in mesoscopic metal wires and at ferromagnet/nonmagnet interfaces

Issues related to "charge-spin coupling" and the diffusive transport of nonequilibrium spin polarized electrons in nonmagnetic materials and at the interface between ferromagnetic and nonmagnetic materials are discussed theoretically. Equations that govern charge and spin transport in three dimensions are derived and appropriate boundary conditions are discussed. These results are applied to a numerical calculation of spin accumulation and diffusion in a two-dimensional Van der Pauw cross. A detailed model of spin transport at ferromagnetic-nonmagnetic metal interfaces is reviewed, the limiting cases of high and low interface conductance are treated, and the relevance of "resistance mismatch" for a variety of experimental systems is analyzed.