Europhys. Lett., 74 (6), pp. 1074-1080 (2006)
DOI: 10.1209/epl/i2006-10053-5

Magnetic properties of free clusters at finite temperatures from first principles

S. Polesya¹, O. Sipr², S. Bornemann¹, J. Minár¹ and H. Ebert<sup>1

1</sup>  Universität München, Department Chemie - Butenandtstr. 5-13 D-81377 München, Germany
²  Institute of Physics, Academy of Sciences of the Czech Republic Cukrovarnická 10, CZ-162 53 Prague, Czech Republic

Hubert.Ebert@cup.uni-muenchen.de

received 26 January 2006; accepted in final form 21 April 2006
published online 17 May 2006

Abstract
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.

PACS
75.50.Tt - Fine-particle systems; nanocrystalline materials.
73.22.-f - Electronic structure of nanoscale materials: clusters, nanoparticles, nanotubes, and nanocrystals.
75.50.Bb - Fe and its alloys.

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