Controlled vortex core switching in a magnetic nanodisk by a rotating field

The control of the vortex state magnetic nanoparticle by ultrafast magnetic fields is studied theoretically. Using the micromagnetic simulations for the Permalloy nanodisk we demonstrate that the vortex core magnetization can be irreversible switched by the alternating field, rotating in the disk plane, with the frequency about 10 GHz and intensity about 20 mT. We propose an analytical picture of such phenomena involving the creation and annihilation of vortex-antivortex pairs and calculate the phase diagram of the fields parameters leading to the switching. (C) 2007 American Institute of Physics.