  We present a formalism determining spin-polarized current and electrochemical
potential inside arbitrary electric circuit within diffusive regime for
parallel/antiparallel magnetic states. When arbitrary nano-structure is
expressed by 3-dimensional (3D) electric circuit, we can determine 3D
spin-polarized current and electrochemical potential distributions inside it.
We apply this technique to (Cu/Co) pillar structures, where pillar is
terminated either by infinitely large Cu layer, or by Cu wire with identical
cross-sectional area as pillar itself. We found that infinitely large Cu layers
work as a strong spin-scatterers, increasing magnitude of spin-polarized
current inside the pillar twice and reducing spin accumulation nearly to zero.
As most experimentally studied pillar structures are terminated by such a
infinitely large layers, we propose modification of standard Valet-Fert
formalism to simply include influence of such infinitely large layers.
