Anisotropy of spin-transfer torques and Gilbert damping induced by Rashba coupling

Strong spin-orbit coupling can manifest itself in the anisotropic character of various magnetic phenomena. Recently, such anisotropy has been observed experimentally for Gilbert damping. The authors perform a microscopic analysis of a paradigmatic two-dimensional model to quantify the anisotropy of spin-transfer torque and Gilbert damping induced by Rashba spin-orbit coupling. Within the model, they derive an unexpected relation between the spin-transfer torque and Gilbert damping terms in the Landau-Lifshitz-Gilbert equation. The authors also introduce the notion of a matrix gauge transformation for the Landau-Lifshitz-Gilbert equation.