The purpose of this work is to combine magnetic nanostructures of two different metals within nanostructured silicon to influence the magnetic switching behavior of the porous silicon/metal nanocomposite. Two routes are used to achieve such nanocomposites. The porous silicon templates are fabricated with a mesoporous morphology offering average pore diameters of 50 nm and these pores are filled with a bi metal filling, namely Ni and Co. The two metals are deposited alternatingly by electrodeposition. A further approach is the chemical growth of Co nanoparticles within porous silicon nanotubes (SiNTs) and the additional deposition of a Ni layer on the outer surface of the tubes (Figure 1). The inner diameter of the silicon tubes is around 50 nm and the wall thickness is about 10 nm. Since the silicon wall of the tubes offers a porous structure the Co particles, which are localized near the pore surface on the wall of a given nanotube, can touch the Ni layer. An alternative structure involves the deposition of an additional Si layer (after the growth of Co particles inside the tubes) as a spacer before the Ni deposition.

These samples have been characterized structurally and magnetically. The magnetic properties of the systems strongly depend on the size and shape of the deposited bi-metal nanostructures and also on the proximity of the Ni and Co structures to each other. If the distance is small enough magnetic exchange coupling between the two metal structures is present. Due to the size of the metal deposits and the coupling of the bi-metal structures the switching behavior of the hysteresis can be tuned. The aim is to achieve self-assembled nanocomposite systems with a high as possible energy product which can be promising for permanent nanomagnets.

Figure 1: SEM image of silicon nanotubes (SiNTs) with Co particles deposited inside the tubes and Ni covering the walls of the tubes.