Spin-Polarized Current Driven Vortex-Pair Switching in a Magnetic Ellipse

Micromagnetic simulations are performed to study the mechanism of vortex core reversal in a Permalloy elliptical element that contains two vortices with opposite polarities. A short current pulse is applied in the film plane along the short axis of the ellipse. The trajectories of the two vortex cores move either clockwise or anticlockwise, depending on the core polarization. Their reversal mechanisms of the two cores are the same through a creation-annihilation process of vortex antivortex pair. By analyzing the partial energies of the sample we find that the core reversal occurs once the maximum local energy density reaches the threshold value (e.g., similar to 3.0 x 10(6) J/m(3) for Permalloy). Interestingly, this energy threshold is a universal constant, irrespective of the applied current strength, vortex polarity and the sample size.