Co and Cr atoms adsorbed to Fe islands on W(110) are investigated with spin-resolved scanning tunneling spectroscopy and first-principles calculations. The spin polarization of the current to Cr adatoms exhibits the same sign as above Fe islands over a wide range of energies. In contrast, it exhibits sign reversals at Co adatoms. These data do not suggest a simple relation between the spin polarization of the current and the orientation of the magnetic moment of the adatom. First-principles calculations reveal that the different spatial decay into the vacuum of majority $s$ and minority $d$ states of the Co adatom is at the origin of the sign reversals of the spin polarization of the current. The different behavior of Cr adatoms is due to their larger exchange splitting and antiferromagnetic coupling to the Fe islands.

• Received 9 January 2012

DOI:https://doi.org/10.1103/PhysRevB.85.155406