Nonequilibrium Quantum Dynamics of Current-Driven Magnetic Domain Walls and Skyrmions

Abstract

Magnetic textures in solid-state nanostructures can be manipulated by an applied electrical current and are thus promising candidates for new classes of electronic devices. The manipulation of a magnetization texture occurs via a spin torque exerted by the spin-polarized current on the local magnetic moments. We present different approaches how to calculate this spin torque under nonequilibrium conditions. In particular, we generalize the conventional approach to calculate the spin torque to treat magnetic structures which have a large spatial gradient (steep structures). We discuss this for the case of ferromagnetic domain walls and show how their chirality can be switched by an external spin-orbit torque. Besides domain walls, we also investigate the dynamics of two-dimensional ferromagnetic skyrmions and derive an equation of motion for the skyrmion’s topological charge density. By this equation we are able to explain the current-induced creation of neutral skyrmion-antiskyrmion pairs which can be used for the production of stable skyrmions after the antiskyrmion partner has disappeared due to dissipation.