Electron correlation effects and magnetic ordering at the Gd(0001) surface

Effects of electron correlation on the electronic structure and magnetic properties of the Gd(0001) surface are investigated using the full-potential linearized augmented plane-wave implementation of correlated band theory (``LDA+U''). The use of LDA+U instead of LDA (local-density approximation) total-energy calculations produces the correct ferromagnetic ground state for both bulk Gd and the Gd surface. Surface strain relaxation leads to a 90% enhancement of the interlayer surface-to-bulk effective exchange coupling. Application of a Landau-Ginzburg-type theory yields a 30% enhancement of the Curie temperature at the surface, in very good agreement with the experiment.