2 Spin and orbital moments on pure Co surface

We have simulated a semi-infinite system of cobalt fcc with (100) or (111) surface. The self-consistent calculations provide the layered resolved spin and orbital atomic moments, see Fig. 6.5. This allows us to establish that there exists an increment of the spin and orbital moments on the cobalt surface and the increment is sensitive to the surface type. Both the spin and the orbital magnetic moments are smaller in the case of the surface (111) than those in the case of the surface (100).

Figure 6.5: The layered resolved spin (left) and orbital (right) moments for a semi-infinite fcc Co(100) and Co(111) system, where the surface is at the atomic layer number 6.
\includegraphics[totalheight=0.272\textheight]{Ms_Co6.eps} \includegraphics[totalheight=0.27\textheight]{Mo_Co6.eps}
The system experiences an increment of the spin and orbital moments on the surface layer, such increment is approximately $ 10\%$ of the bulk value in the case of Co(100) surface and $ 5\%$ in the Co(111).

It is well known that the orbital moments of a delocalized state closely depend on the shape and the width of the density of states (DOS). The main reason for an increment of the orbital and spin moments at the surface is the modification of DOS [161]. This can have different origins as for example:

(i)
The reduction of the crystal field at the surface leads to an enhancement of the orbital moment.
(ii)
The d band becomes narrower at the surface due to the reduce number of nearest-neighbors.

Rocio Yanes