3 "Ab-initio" modeling of bulk Co and its interfaces

The "ab-initio" calculations presented in this thesis are based on the fully relativistic Screened Korringa-Kohn-Rostoker (SKKR) Green's function method [86]. Within this method the spin-polarization and the relativistic effects are treated on equal theoretical footing by solving the Kohn-Sham-Dirac equation. We used the local spin-density approximation (LSDA) for the exchange-correlation term and the effective potential and field were treated within the atomic sphere approximation (ASA), with an angular momentun cutoff of $ l=2$.

In ASA the effective potential is of a muffin-tin type, surrounding each atom there is a sphere of radius $ S_{MT}$ outside of which the potential has a value equal to a constant, and within the sphere the potential is assumed to be spherically symmetric leaving only a radial dependence of the potential. Within ASA , the effective potential $ V_{eff}$, at one atomic site can be written as:

$\displaystyle V_{eff}\approx V_{MT}=\Bigl\{\begin{array}{cccc} v(r) & r & \leq & S_{MT} \ V_{MTZ} & r & > & S_{MT}, \end{array}$ (93)

here $ V_{MT}$ is the Muffin-Tin potential, where $ V_{MTZ}$ is the muffin-tin zero potential, which is defined as the value of the muffin-tin potential at a distance $ S_{MT}$ ( $ V_{MTZ}=v(r=S_{MT})$) and $ v(r)$ is the spherical potential inside the muffin-tin sphere.

Henceforth we will apply a spin-polarized relativistic version of the screened Korringa-Kohn-Rostoker Green's function method to calculate the magnetic properties: spin and orbital moments, exchange constants, and magnetocrystalline anisotropy energy. Once reached this point, we would like to point out some issues, which will be important throughout this chapter:

The theoretical and computational details of the SKKR method used in our calculations can be found in the Weinberger book [155].

First we will discuss the results of a self-consistent calculation of the work function, the spin and orbital moments in the $ Co/Ag$ layered system, after that we will analyze the results for the exchange interaction and the magneto-crystalline anisotropy (MCA) energy, obtained using the "magnetic force theorem". Finally we will study the magnetic behavior of a particular system $ Co(111)\setminus Ag_{1}$ with the temperature.

Rocio Yanes