Evidence for imperfect ferromagnetic coupling between the Gd(0001) surface and the bulk

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Abstract
The authors have investigated ordered Gd(0001) films deposited on W(110) by spin-polarized photoemission at temperatures well below the Curie temperature. The gadolinium valence band including the 5d surface state, the 5d bulk, the 4f levels and the background exhibit considerable spin polarization along the same direction in the plane of the film, indicative of ferromagnetic coupling between the surface and the bulk. The 4f spin-polarized photoemission data provide strong evidence that the surface 4f polarization differs from the bulk 4f polarization for Gd(0001). They attribute the differences between surface and bulk polarizations to a component of magnetization normal to the surface in the surface magnetization which is not present in the bulk. Dilute amounts of contamination at the surface result in a more perfect ferromagnetic coupling between the surface and the bulk.