Two types of magnetic vortex cores in elliptical permalloy dots

Elliptical (track-shaped) permalloy (Ni19Fe81) dots, in which magnetic circular vortex and antivortex structures are stabilized, were prepared and the magnetic properties of perpendicular magnetization spots (turned-up magnetizations) at the cores of both types of vortices were studied. Using magnetic force microscopy, the direction of the turned-up magnetization was detected and the switching field was measured. It was found that the value of the switching field of the turned-up magnetization at the antivortex core is smaller by about 1000 Oe than that at the circular vortex core. It was confirmed that the switching of the turned-up magnetization in the antivortex is not influenced by the directions of the turned-up magnetizations in the neighboring circular vortices. Vanishing and regenerating processes of turned-up magnetizations were observed by increasing and decreasing the magnetic field applied to the in-plane direction.