Structural and electronic properties of magnetic cylinders at the atomic scale

There has been a great deal of work concerning cylindrical magnetic nanoparticles in the last decade due to a variety of experimental techniques to grow them. On the other hand, most the theoretical work is based on macroscopic approximations which might find limitations when a lower scale is approached. In the present article we try to fill in this gap using electronic structure calculations to get an initial picture of what are the properties of such structures at the molecular level studying clusters of Co atoms with cylindrical shape. The usual SIESTA program is invoked to study several structures looking for stability and establishing their properties. It turns out that not all possible cylinders are stable. However, several stable structures are found without apparent limitations of size. We report energies, distances, coordination numbers and magnetic moments for the atoms in the 25 stable cylindrical clusters optimized here. One of the important results reported and discussed is that magnetization is not uniformly distributed within the cylinders at this scale which opposes the usual macroscopic assumption which considers uniform magnetic distribution through the objects. Other differences with respect to nanoscopic or macroscopic magnetic cylinders are also discussed.