Manifestation of nonconservation of magnetization modulus in the steady-state domain wall motion

The influence of the nonconservation of magnetization modulus on the steady-stale domain wall motion is investigated, The wall motion in the presence of an external field normal to the anisotropy axis is considered. The Slonczewski-type equations are derived from the Landau-Lifshitz equation with relaxation term introduced by Bar'yakhtar. It is shown that the nonconservation of magnetization modulus gives a larger contribution to the wall drag in ferromagnets with a narrower ferromagnetic resonance line width than in those with a wider line width. It is also shown that the standard Landau-Lifshitz-Gilbert equation gives almost the same results for the wall velocity in ferromagnets with wider resonance line if the value phenomenological relaxation constant is determined from domain wall mobility measurements, instead of data on ferromagnetic resonance line width.