Simulation de dispositifs pour la nano-spintronique

Abstract

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.