Magnetic properties of free Fe clusters at finite temperatures from first principles

An ab initio theoretical investigation on the finite-temperature magnetism of free metallic clusters is presented. The exchange coupling between local magnetic moments in Fe clusters of 9-89 atoms was calculated within the multiple-scattering formalism. From the results an effective classical Heisenberg Hamiltonian was constructed, and the magnetization as a function of temperature was obtained via Monte Carlo simulations. It is found that the effective critical temperature is not a monotonous function of the cluster size. We demonstrate that for a proper description of finite-temperature magnetism of free clusters, the site dependence of the exchange coupling must be taken into account.