Controlling magnetic vortices through exchange bias

The magnetic behavior of exchange coupled ferromagnetic (FM) -anti-ferromagnetic (AFM) disks, with composition Ta(5nm)/Py(12nm)/IrMn(5nm)/Pt(2nm), where Py, which denotes Permalloy (i.e., NiFe) is FM and IrMn is AFM, with micron and submicron diameters, is investigated. These structures exhibit different magnetization reversal mechanisms depending on the direction of the applied magnetic field. Such behaviors are studied by means of magneto-optic Kerr effect, magnetic force microscopy imaging and micromagnetic simulations. Exchange coupling with IrMn can also result in an enhancement of the vortex stability with respect to Permalloy disks without the AFM, when the disks are zero-field cooled (ZFC) from above the blocking temperature of the system. This enhanced stability manifests itself by an increase of both the nucleation and annihilation fields of the vortex. Such effect is ascribed to an imprint of the vortex structure into the AFM during the ZFC through the blocking temperature.