transverse spin accumulation without changing the longitudinal polarization of the current. No such change occurs in the model in Ref. , casting doubt on the validity of the form of the spin flip scattering assumed there.

Microscopic considerations also argue against this form of the relaxation. As we have emphasized, the natural basis for an electron spin moving though a non-collinear magnetization is not along the local exchange field ${\bf B}_{\rm ex}(x)$, but rather along a local effective field ${\bf B}_{\rm eff}(x)$, which includes the corrections due to the gradient of the magnetization \[see Eq. (\[eqn:gradientfield\])\]. Any spin that deviates from parallel or antiparallel alignment with the effective field will precess around the effective field, and on average will point parallel or antiparallel. Thus, we expect that there is [*no*]{} tendency for electron spins moving in a non-uniform magnetization to align themselves with the local exchange field ${\bf B}_{\rm ex}(x)$ by spin-flip scattering (or any other mechanism). Rather, the adiabatic solution is precisely alignment of their spins with the local effective field ${\bf B}_{\rm eff}(x)$. Without further microscopic justification, we believe that the phenomenological form of spin flip scattering assumed in Ref.  should not be used in systems with non-collinear 