Local probing of vortex core movement in a Ni-Fe disk using magnetic field sweeping-magnetic force microscopy

We have studied the magnetization reversal in a 40-nm-thick Ni-Fe disk with a diameter of 600nm using magnetic field sweeping (MFS)- magnetic force microscopy (MFM). All the points within the disk, which are perpendicular to the magnetic field, show marked changes in phase as the magnetic field is varied. These results demonstrate that the vortex core nucleates at the disk edge, moves quickly around a point which is 100nm away from the center of the disk, moves from that point to the opposite disk edge, and further annihilates at that edge. Additionally, at local points near the disk edge, at which the vortex core annihilates, a sharp phase decrease or increase is observed as the magnetic field is varied, caused by the chirality of the vortex core in the disk. Therefore, it is concluded that the detailed vortex core movement in a disk can be successfully observed using MFS-MFM.