Features of unidirectional magnetic anisotropy in multilayer nanostructured systems [Co-Al2O3]

We study the magnetic anisotropy of multilayer nanostructures [Co-Al2O3]N with fixed Co island layer thickness (d approximate to 1.2 nm) and varying Al2O3 layer thickness. We use the Kerr effect to measure the magnetization hysteresis loops at different orientations of the magnetic field. We observed a unidirectional magnetic anisotropy in structures with small thicknesses of Al2O3 layers (d < 1.4 nm) when the exchange interaction between the Co layers is large. This anisotropy was oriented at 150<degrees> with respect to the easy axis of a continuous Co film. We believe that the unidirectional anisotropy can be caused by the super-vortex magnetization of the multilayer structure, while the unidirectional magnetization is caused by the projection of the super-vortex core on the sample plane.