Nanospheres generate out-of-plane magnetization

Large arrays of ordered magnetic nanostructures have been fabricated by sputter depositing Fe/Gd multilayers on an array of self-assembled nanospheres. On a planar substrate the system shows an in-plane magnetization whereas a spin reorientation transition (SRT) to out-of-plane orientation occurs on the spherules. This SRT cannot only be explained by the reduction in the shape anisotropy due to patterning of the extended film into nanometer sized islands. In fact, more important is the curved surface of the film on the nanocaps. Micromagnetic simulations of various geometries reveal that the crescent shape of the magnetic film on the spheres is ideal to get small values of the shape anisotropy for all diameters of the spheres, ranging from 1 μ m down to 20 nm. The observed SRT enables a simple and cost effective bottom-up approach to produce patterned perpendicular magnetic nanostructures, having a high potential for magnetic data storage and spintronic applications.