The motion of simple domain walls and of more complex magnetic textures in the presence of a transport current is described by the Landau-Lifshitz-Slonczewski (LLS) equations. Predictions of the LLS equations depend sensitively on the ratio between the dimensionless material parameter β which characterizes non-adiabatic spin-transfer torques and the Gilbert damping parameter α. This ratio has been variously estimated to be close to 0, close to 1, and large compared to 1. By identifying β as the influence of a transport current on α, we derive a concise, explicit and relatively simple expression which relates β to the band structure and Bloch state lifetimes of a magnetic metal. Using this expression we demonstrate that intrinsic spin-orbit interactions lead to intra-band contributions to β which are often dominant and can be (i) estimated with some confidence and (ii) interpreted using the ``breathing Fermi surface'' model.
Citation: Physical Review B (Condensed Matter and Materials Physics)
Pub Type: Journals
Spin-transfer torque, Magnetic damping, Magnetization dynamics, Adiabatic, Spin-orbit coupling, Domain wall, Spin current