Magnetization reversal in patterned double-vortex structures

The magnetization reversal process for micron and submicron disk-shaped dots is controlled by successive nucleation, displacement, and annihilation of a magnetic vortex. Here the reversal process for a system involving two ferromagnetic disks separated by a nonmagnetic spacer is investigated experimentally, analytically, and numerically. Permalloy (Ni80Fe20 or Py) dots with thicknesses of up to 40 nm and diameters of 0.5-2.5 mu m separated by a copper spacer (1-45 nm thick) were considered. Micromagnetic simulations indicate that the disks will each support oppositely directed vortices at remanence and also show the hysteresis of the coupled structures. The calculations are compared to hysteresis loops and x-ray photoemission electron microscopy images of Py/Cu/Py dots produced by electron-beam lithography and magnetron sputtering. (c) 2005 American Institute of Physics.