Magnetic antivortex dynamics in a two nanocontact disk

摘要

Stable magnetic vortex-antivortex-vortex structures can form on a thin ferromagnetic disk at two separated nanocontacts with the vortices at the nanocontacts and the antivortex between the nanocontacts. When the vortices are pinned to the nanocontacts, the antivortex gyrotropic motion can be isolated about the stable equilibrium between the pinned vortices. The restoring force in the antivortex is from the combined exchange, magnetostatic, and Oersted fields where the exchange and the magnetostatic interactions will result in an attractive vortex-antivortex force, but the net Oersted field from the nanocontacts tends to stabilize the antivortex between both nanocontacts. A small ac driving current on one of the nanocontacts provides an efficient driving force for this antivortex oscillator that is tunable through the nanocontact current. Owing to the competing magnetostatic and Oersted forces, the oscillator can be soft along the direction between the nanocontact resulting in a high amplitude oscillation. Moreover, because of this competition, nonlinear effects are important at low ac current amplitudes. An interesting nonlinear effect is an amplitude jump that is shown to be a result of a time-dependent asymmetry of the antivortex potential.