Magnetic vortices in magnetic nano-caps formed on densely packed particle array

When the size of a magnetic structure becomes comparable to a critical length scale, such as exchange length, the multidomain spin configuration becomes energetically unfavorable and either a single domain or an inhomogeneous magnetization configuration is formed. One example is a magnetic vortex state [1], which is of considerable technological interest due to its unique physical properties, such as low magnetic stray field and high integration density. A magnetic vortex is characterized by the in-plane magnetic flux closure, which can rotate clockwise or counterclockwise and the direction of the out-of-plane vortex core polarization, which can point up or down [2]. The reversal mechanism of a magnetic vortex is to a large extending controlled by the contributions of exchange and magnetostatic energy. Thus, additional exchange coupling induced by an antifer-romagnetic layer [3,4] can be used to alter these properties.