Résumé:
One of the questions addressed in the spintronics field is to find a new materials
that can be semiconductor and magnetic at the same time. Our thesis contains two
studies: The first consists in an electronic and magnetic properties study for magnesium
oxide MgO doped with manganese Mn, with the use of the full potential linearized
augmented plane wave method (FP LAPW). We have compared two approaches, the
spin polarized local density approximation (LSDA) and LSDA+U which take into account
the strong correlation between d electrons of transition metals by adding Hubbard
correction. In both approximations we were able to highlight the transition from highspin
state (5/2 solution) to the low-spin state (1/2 solution) by simple reduction of the
lattice parameter. The high spin state remains an insulator whereas the low spin state
very interesting, gives rise to a half-metallic material where we can avoid the Jahn-Teller
effect. In the second study, we developed a model for two quantum dots (two orbitals) in
parallel configuration, connected to two electrodes where we have neglected the
ferromagnetism of the electrodes. We expressed the self-consistent equations for each
state using the non-crossing approximation (NCA) then place in a program designed for
a single dot. The calculation of Green functions allowed us to have access to the spectral
functions for different filling of the two dots. The results were verified as part of the
electron-hole symmetry and compared with the atomic limit.
