Spin currents in ferromagnets

Using a density matrix formulation for the effective action, we have obtained a set of macroscopic equations that describe the spin accumulation in a non-homogeneous ferromagnet. We consider the application of these macroscopic equations to a situation where there has been an apparent contradiction between fluid and quantum-mechanical results. We show that in this case spin accumulation is an interface effect, confirming earlier quantum-mechanical results and resolving the discrepancy