Geometrical effects on the magnetism of small Ni clusters

Abstract

A self-consistent tight-binding method has been used to calculate the average magnetic moments \ensuremath{\mu}-bar of ${\mathrm{Ni}}_{\mathrm{N}}$ clusters between N=5 and 16. The geometrical structures were taken from the results of molecular-dynamics simulations with semiempirical potentials. The agreement with experiment (minima of \ensuremath{\mu}-bar at N=6 and 13, and a maximum for N=8) is good, and the variations of the average magnetic moment are explained as a consequence of geometrical effects: low coordinated atoms have large magnetic moments. Furthermore, the deviation of the interatomic distances from a smooth behavior also influences the magnetic moments. The contribution of the sp electrons to the magnetism is found to be relevant for Ni clusters with less than ten atoms.