Characterization of the magnetization vortex state in magnetic tunnel junctions patterned into nanometer-scale arrays

The aim of this work is to investigate the switching characteristics of magnetic tunnel junctions (MTJs) that contain two ferromagnetic layers in a magnetization vortex state as a function of the aspect ratio (length/width). Magnetic tunnel junctions NiFe 30 nm ∕ AlOx 1.3 nm ∕ Co 15 nm have been patterned into arrays of dots with identical geometries as in a single layer having a vortex state at low aspect (width/length) dots. The switching characteristics were studied using a vibrating sample magnetometer and magneto-optic Kerr effect techniques. The results show the relation between the switching fields and the sizes of the MTJ dots in which the switching of the two ferromagnetic layers is indistinguishable at low aspect ratio. It was found that as the aspect ratio increases, the switching becomes more distinguishable. This can be attributed to the magnetization vortices in the two ferromagnetic layers and the magnetostatic coupling (dipole-dipole interaction), which are size-dependent.