2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/126274We have investigated, by the Monte Carlo simulation, spin systems which represent moments of arrayed magnetic nanoparticles interacting with each other only by the dipole-dipole interaction. In the present paper we aim the understanding of finite size effects on the magnetic nanoparticles arrayed in hexagonal columns cut out from the close-packing structures or from those with uniaxial compression. In columns with the genuine close-packing structures, we observe a single vortex state which is also observed previously in finite 2-dimensional systems. On the other hand in the system with the inter-layer distance set $1/\sqrt{2}$ times of the close-packing one, we found ground states which depend on the number of layers. The dependence is induced by a finite size effect and is related to a orientation transition in the corresponding bulk system.3 pages, 2 figures. Proceedings of the International Conference on Magnetism 2006 (ICM2006) conference. To appear in a special volume of Journal of Magnetism and Magnetic MaterialsStatistical MechanicsMaterials Sciencetext