Structure and magnetic properties of (Fe2O3)n clusters (n=1-5)

Global minimum structures of neutral (Fe2O3)(n) clusters with n = 1-5 were determined employing the genetic algorithm in combination with ab initio parameterized interatomic potentials and subsequent refinement at the density functional theory level. Systematic investigations of magnetic configurations of the clusters using a broken symmetry approach reveal antiferromagnetic and ferrimagnetic ground states. Whereas (Fe2O3)(n) clusters with n = 2-5 contain exclusively Fe3+, Fe2O3 was found to be a special case formally containing both Fe2+ and Fe3+. Calculated magnetic coupling constants revealed predominantly strong antiferromagnetic interactions, which exceed bulk values found in hematite. The precise magnetization (spin) state of the clusters has only small influence on their geometric structure. Starting from n = 4 also the relative energies of different cluster isomers are only weakly influenced by their magnetic configuration. These findings are important for simulations of larger (Fe2O3)(n) clusters and nanoparticles.