Vortex rotation control in Permalloy disks with small circular voids

We studied the magnetization reversal of Permalloy disks with a small circular void either concentric or decentered. In both systems the reversal takes place via the nucleation and annihilation of a magnetic vortex. By applying the diffracted magneto-optic technique combined with numeric micromagnetic simulations we retrieved the information about the sense of rotation of the magnetization in the vortex state. For the disks with the concentric void no preferential rotation has been observed. For the case of decentered void, the sense of rotation of all probed disks is deterministically controlled by appropriately choosing the direction of the externally applied field and the void position with respect to the disk center