Domain-wall dynamics driven by adiabatic spin-transfer torques

In a first approximation, known as the adiabatic process, the direction of the spin polarization of currents is parallel to the local magnetization vector in a domain wall. Thus the spatial variation of the direction of the spin current inside the domain wall results in an adiabatic spin-transfer torque on the magnetization. We show that domain-wall motion driven by this spin torque has many unique features that do not exist in the conventional wall motion driven by a magnetic field. By analytically and numerically solving the Landau-Lifshitz-Gilbert equation along with the adiabatic spin torque in magnetic nanowires, we find that the domain wall has its maximum velocity at the initial application of the current but the velocity decreases to zero as the domain wall begins to deform during its motion. We have computed domain-wall displacement and domain-wall deformation of nanowires, and concluded that the spin torque based on the adiabatic propagation of the spin current in the domain wall is unable to maintain wall movement. We also introduce the concept of domain-wall inductance to characterize the capacity of the spin-torque-induced magnetic energy stored in a domain wall. In the presence of domain-wall pinning centers, we construct a phase diagram for the domain-wall depinning by the combined action of the magnetic field and the spin current.