Effect of S segregation on the surface magnetism of Fe(100)

Bulk impurities of the ferromagnetic transition metals segregate at the surface at moderate temperature and severely modify the surface magnetic properties. S segregation on Fe(100) produces a stable c(2x2) reconstruction at 600 degrees C. We have measured the change of the magnetic properties of Fe(100) due to the formation of the c(2x2)S surface by measuring the exchange coupling along a path perpendicular to the surface via the spin-wave stiffness and the relative change of the iron surface magnetic moment by photoemission magnetic dichroism experiments and spin-polarization measurements of the secondary yield. A stronger coupling between the c(2x2)S surface and the bulk then for the clean Fe(100) free surface is found. Changes of the Fe 3p core hole magnetic splitting show that the surface magnetic moment of Fe is reduced by up to 20% upon S segregation with respect to the clean surface. Strong magnetic dichroism of the electron states just below the Fermi level indicates a filling of the surface minority spin band in the c(2x2)S/Fe(100) surface relative to the clean Fe(100) surface.