Spin Accumulation and Domain Wall Magnetoresistance in 35 nm Co Wires

An enhancement of the resistance due to the presence of only one or two isolated domain walls is clearly evidenced by transport measurements in 35 nm epitaxial Co wires, $20\mu \mathrm{m}$ long. The deduced relative change in the resistivity is at least 1 order of magnitude larger than the one predicted from a model based on the mixing of spin channels occurring over the length scale of the domain wall width [P. M. Levy and S. Zhang, Phys. Rev. Lett. 79, 5110 (1997)]. This inconsistency can be resolved by taking the effect of spin accumulation into account, which scales in the case of Co over the much larger distance of the spin diffusion length.