Dynamics of vortex-antivortex matter in nanostructured ferromagnet-superconductor bilayers

Abstract

We investigate theoretically the dynamics of vortices and antivortices in a hybrid superconductor magnetic-dot-array bilayer with the nanodots polarized in plane. Our model naturally accounts for creation and annihilation of vortex-antivortex (v-av) pairs and simulate their motion by a (Langevin) molecular-dynamics algorithm. We observed several phenomena resulting from the intricate vortex-antivortex dynamics in this system. In general, as a dc-transport current is applied, the steady state corresponds to a cyclic sequence of vortex-antivortex creation, motion and annihilation processes, giving rise to periodic fluctuations of the number of v-av pairs and the induced electric field. Surprisingly, the v-av motion does not follow, in general, the induced Lorentz force direction. Hence, a vortex-guidance effect and the resulting transverse electrical field were observed at zero external magnetic field when the current was applied near certain high-symmetry directions.