Influence of temperature on the systematics of magnetic moments of free Fe clusters

We investigate how temperature affects the dependence of the average magnetic moments ¯ μ of clusters on their size and how the magnetic moment profile of an individual cluster varies with temperature T . The focus is on free spherical Fe clusters of 9–89 atoms. The interaction among individual magnetic moments is described by a classical Heisenberg spin Hamiltonian, with exchange coupling constants provided by ab initio calculations. Average magnetic moments ¯ μ for finite T were obtained via Monte Carlo simulations. We found that the exchange coupling depends on the cluster size and on the position of the atom in the cluster in a complex way, with no obvious systematics. The magnetic moment profile of an individual cluster becomes more uniform if T increases. The dependence of ¯ μ on the cluster size, in practice, does not depend on temperature if T is in the range of 0–300 K. Ground-state calculations for T = 0 K should thus be able to describe experiments based on the deflection of a molecular beam in a magnet for T � 0K . (Some figures in this article are in colour only in the electronic version)