Rashba spin torque in an ultrathin ferromagnetic metal layer

In a two-dimensional ferromagnetic metal layer lacking inversion symmetry, the itinerant electrons mediate the interaction between the Rashba spin-orbit interaction and the ferromagnetic order parameter, leading to a Rashba spin torque exerted on the magnetization. Using Keldysh technique, in the presence of both magnetism and a spin-orbit coupling, we derive a spin diffusion equation that provides a coherent description to the diffusive spin dynamics. The characteristics of the spin torque and its implication on magnetization dynamics are discussed in the limits of large and weak spin-orbit coupling.