Interdependence of shape and magnetic properties in Al-nanoparticles doped with Ni and Pt

By means of ab initio calculations, including spin-restricted Born-Oppenheimer molecular dynamics at finite vibrational temperature, we investigate the magnetic behaviour of Al, AlNi and AlPt nanoparticles of 19 atoms. Starting from a poly-icosahedron, we observe that the 5-fold symmetry axis is usually preserved at 100 K, but a few dynamical structural transformations take place towards three new architectures characterized by a different piling of the pentagon rings around the 5-fold axis. Other shapes, such as the interplay of an octahedron to an icosahedron, could be detected although less frequently. Notwithstanding a ferromagnetic behaviour is observed independently of shapes and chemical compositions, a depletion of the total magnetisation occurs when the surface is delimited by (100) facets, or by distorted (100) facets, associated with the appearance of an antiferromagnetic ordering.