Micromagnetic modelling of soliton mode in in-plane ferromagnets

Non uniform magnetization configurations have been found to be the underlying cause of most of the phenomena arising in the field of magnetic nanostructures in the last years. Non-uniform configurations are presented not only in the micrometer sized sensors, or open point contact spin-transfer driven nano-oscillators (STNOs), but also in spin valves (SVs) with dimensions in the range of a hundred nanometers. Injection of a direct electrical current through SVs offers the possibility to induce microwave steady-state magnetization precession by the action of the spin transfer torque. In particular, circular vortex and antivortex motion can be excited by a direct spinpolarized current as recently demonstrated both experimentally and by means of micromagnetic simulations.[1] Here, we present a complete full micromagnetic study on the vortex dipole dynamics in different kinds of sub-micrometer SVs where the current is injected through a nano-aperture of tenths of nanometers(fig1 top-left). All the features predicted by the first analytical models are reported, including vortex dipole rotation or translation depending on the shape (elliptical (fig.1a), circular(fig.1b), rectangular(fig.1c)) and size of the SV and also on the field and/or current.