Physics – Condensed Matter – Strongly Correlated Electrons
Scientific paper
1999-08-13
Physics
Condensed Matter
Strongly Correlated Electrons
6 pages, RevTeX, 4 eps figures, accepted (Phys. Rev. B), for related work and info see http://orion.physik.hu-berlin.de
Scientific paper
10.1103/PhysRevB.60.12861
The stability of ferromagnetism at the surface at finite temperatures is investigated within the strongly correlated Hubbard model on a semi-infinite lattice. Due to the reduced surface coordination number the effective Coulomb correlation is enhanced at the surface compared to the bulk. Therefore, within the well-known Stoner-picture of band ferromagnetism one would expect the magnetic stability at the surface to be enhanced as well. However, by taking electron correlations into account well beyond the Hartree-Fock (Stoner) level we find the opposite behavior: As a function of temperature the magnetization of the surface layer decreases faster than in the bulk. By varying the hopping integral within the surface layer this behavior becomes even more pronounced. A reduced hopping integral at the surface tends to destabilize surface ferromagnetism whereas the magnetic stability gets enhanced by an increased hopping integral. This behavior represents a pure correlation effect and can be understood in terms of general arguments which are based on exact results in the limit of strong Coulomb interaction.
Herrmann Todd
Nolting Wolfgang
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