The magnetization reversal in Permalloy (Py) and Py-IrMn disks (1 μm diameter) is investigated. The Py disks reverse their magnetization via vortex state formation. Conversely, if the Py-IrMn disks are field cooled from above the blocking temperature TB, a critical angle with respect to the cooling direction is set, beyond which the vortex no longer nucleates. This angle can be experimentally tuned by varying the magnitude of the exchange bias field. Furthermore, the coupling with IrMn can also induce an enhancement of the vortex stability when the disks are zero-field cooled from above TB. © 2006 American Institute of Physics.