Spin-transfer torque in disordered weak ferromagnets

We study theoretically the spin-transfer effect on a domain wall in disordered weak ferromagnets. We have identified the adiabatic condition for the disordered case as lambda lambda(D)equivalent to hD/Delta(sd), where D and Delta(sd) are the diffusion constant and the spin splitting energy due to the sd type exchange interaction, respectively, and found out that perfect spin-transfer effect occurs even in weak ferromagnets as long as this condition is satisfied. The effective beta term arising from the force turns out to govern the wall dynamics, and therefore, the wall motion can be as efficient as in strong ferromagnets even if Delta(sd) is small.