  The substrate contribution to the magnetic anisotropy energy (MAE) of
supported nanostructures can be quantified by a site-selective manipulation of
the spin-orbit coupling (SOC) and the effective exchange field B_ex. A
systematic study of Co adatoms and Co monolayers on the (111) surfaces of Cu,
Ag, Au, Pd and Pt is performed to study common trends in this class of
materials. It is found that for adatoms, the substrate contribution is
relatively small (10-30% of the MAE) while for monolayers, the substrate
contribution can be substantial. The contribution from the SOC is much more
important than the contribution from the exchange field B_ex, except for highly
polarizable substrates with a strong SOC (such as Pt). The substrate always
promotes the tendency to an out-of-plane orientation of the easy magnetic axis
for all the investigated systems.
