Exchange interaction and local environment effects on the magnetic properties ofFeNclusters

The magnetism of ${\mathrm{Fe}}_{\mathrm{N}}$ clusters is studied by using a d-band Hubbard-like Hamiltonian in the unrestricted Hartree-Fock approximation. The local magnetic moments, magnetic order, and average magnetization per atom are calculated for T→0 as a function of the intra-atomic Coulomb exchange integral J. Different cluster sizes and structures are considered and local environment effects are analyzed. Both continuous and sharp (first-order-like) transitions in the local magnetic moments are obtained as a function J, which are related to changes in the local densities of electronic states and to redistributions of the spin-polarized charge density. Finite-size and structural effects are discussed, particularly by comparison with bulk results.