Magnetotransport in nanostructures: The role of inhomogeneous currents

In the study of electronic transport in nanostructures, electric current is commonly considered homogeneous along the sample. We use a method to calculate the magnetoresistance of magnetic nanostructures where the current density may vary in space. The current distribution is numerically calculated by combining micromagnetic simulations with an associated resistor network and by solving the latter with a relaxation method. As an example, we consider a Permalloy disk exhibiting a vortex-like magnetization profile. We find that the current density is inhomogeneous along the disk, and that during the core magnetization reversal it is concentrated toward the center of the vortex and is repelled by the antivortex. We then consider the effects of the inhomogeneous current density on spin-torque transfer. The numerical value of the critical current density necessary to produce a vortex core reversal is smaller than the one that does not take the inhomogeneity into account.