Inversion of spin polarization above individual magnetic adatoms

Using a cryogenic scanning tunneling microscope, the spin-resolved differential conductance through a magnetic tunnel junction consisting of a Cr tip, a vacuum barrier, and a single Co adatom on a Co monolayer is measured. It is proved, that the spin polarization at the Fermi level above this atomic protrusion is reversed with respect to the atomically flat Co layer, and thus dominated by majority electrons. Experiments with the same Cr-tip electrode and Co adatoms or dimers on Pt(111) as the second electrode suggest that the inversion might be unique for single atomic protrusions due to the reduced coordination.