Magnetism and the potential energy hypersurfaces of Fe53 to Fe57

We investigate magnetic and structural properties of iron clusters from Fe53 to Fe57 around the first peak in the experimental magnetic moment data at Fe55. A density-functional based tight-binding scheme, fully incorporating the effects of spin-polarization and charge transfer in a self-consistent manner, has been used. The potential hypersurfaces have been scanned by an unconstrained search using a genetic algorithm. We find icosahedral structures to be energetically favorable. These clusters show non-ferromagnetic spin-ordering leading to small average magnetic moments in their ground states. We establish a connection between the magnetic moments and the perturbation of icosahedral symmetry. This is interpreted further on the level of atomic spin-populations by examining the magnetic behavior of the Fe55 icosahedron.