Experimental observation of switching in ferromagnetic nanoscale double disks

We investigated a system of two overlapping ferromagnetic permalloy disks, called a hysteron. For sufficiently small disk diameters the hysteron contains only one vortex which is displaced off the center of the disk hosting it. By swapping the vortex from one side of the disk to the other via an in-plane magnetic field, the magnetization in the appended disk is reversed. The magnetization reversal process based on these off-center magnetic vortex states was theoretically found to have low switching fields, as magnetization reversal does not require wall nucleation. Here we investigate hysterons experimentally by studying magnetization reversal and configuration by means of Lorentz transmission electron microscopy and electron holography. For the smallest hysterons with individual disk diameters below ~2000.3em0exnm we found the peculiar switching scheme suggested recently.