| This dissertation addresses the construction of a simple model, based on the Fermi liquid theory, for the description of the thermodynamics and spin dynamics of the half-metallic ferromagnetic systems. A half-metallic ferromagnet (HMF) is a material in which at T = 0, spin-up electrons behave like electrons in a metal whereas spin-down electrons behave like electrons in an insulator. In recent years, HMFs have received special attention, in the new field of spintronics, as sources and filters for spin polarized currents and some of them for displaying dramatic colossal magnetoresistance effects. HMFs have been extensively studied in the band theory approach. In general, the agreement with experiment is remarkable; however, the band-theory-predicted electronic specific heat is consistently smaller than the experimental value. A microscopic approach has also been developed and explains the discrepancy in the specific heat as due to non-quasiparticle contributions. As a consequence, it has been argued that Fermi liquid theory is not sufficient to describe HMFs. Contrary to this statement, in this dissertation, we have shown how a phenomenological approach based on the Fermi liquid theory for spin polarized systems, accounts for the observed enhancement in the electronic specific heat. Therefore, it includes the correlations missed by density functional theory. Furthermore, when applied to the description of the spin dynamics, it shows the existence of a gapless mode and gives the corresponding spin stiffness in a way which is consistent with experiment. |
