Analysis of the energy distribution of iron nano-spheres for bit-patterned media

Improved magnetic memory systems belong to the main research topics in spintronics. Here we show micromagnetic simulations used to analyze the energy density of nano-scaled iron spheres. Layers of different thickness, partly coated with iron oxide, were tested in terms of spatial uniformity of the physical system energy. For a single non-coated or iron-oxide coated droplet, the spatial distribution of the total energy is not uniform and depends on the nano-droplet size. Additionally, for systems consisting of four objects, the relation between relative distance and the resultant magnetization distribution was analyzed. The mutual relation between droplet size and the underlying magnetization distribution as well as the character of local energy extrema was investigated. The size changes for the four-droplet system were compared with the single object behavior to obtain a criterion for the minimum distance between spheres to behave as a single object. The calculations revealed that the oxidized spheres could be placed closer to each other in comparison to the non-coated system. For the proposed oxide coated system, the increase of this maximum packing density is equal to about 12%, as compared to the non-coated system.