First-principles Study On Several Novel Functional Magnetic Materials

For the quantum mechanics, we know that the electron has charge and spin properties. Our previous studies mainly focused on the electronic properties of charge, as well as we developed the traditional semiconductor physics, but we ignored the electronic properties of spin.In the past twenty years, electronic spin has attracted more and more research interest, and a new field of semiconductor spintronics was formed. Compared to the traditional semiconductor devices, the spintronics devices have the advantages of smaller size, lower energy consumption, and quick working speed, and it can also produce new devices combining the electronic spin and charge, the potential application is very great. Diluted magnetic semiconductors and half-metallic ferromagnets are important materials used in spintronics devices, and it is a hot studying field in condensed matter physics and materials physics.In Chapter3, we investigated the volumes, electronic structures, and magnetic properties of sp type binary half-metallic ferromagnets CaC, SrC, and BaC of rocksalt structure as pressure increases. The magnetic moments, lattice constants, and total energies as function of pressure are calculated. The magnetic moment decreases with increasing pressure. It is thought that the main reason for the magnetic transitions of these compounds is the band widening of anion p states.In Chapter4, we investigate the volumes, electronic structures, and magnetic properties of sp type binary half-metallic ferromagnets SrC and BaC of zinc-blende structure with charge doping. The magnetic moments, lattice constants, and orbital populations as function of doping level are calculated. The calculations predict that the geometric, electronic, and magnetic structures of these compounds are changed drastically upon electron and hole doping.In Chapter5, we investigate the volumes, electronic structures, and magnetic properties of sp type ferromagnetic electrides K, Rb, and Cs. The magnetic moments, lattice constants, and total energies as function of pressure are calculated. The calculations exhibit the occurrence of both ferromagnetism enhancement and collapse as pressure increases and illuminate that the spin polarized interstitial electron blobs are formed by both s and p electrons. The distortion and nesting of the Fermi surface is also presented with increasing pressure.In Chapter6, we confirmed a new path for the formation of.sp-ferromagnetic states: interstitial nonmagnetic atoms. The fluorine and hydrogen interstitials in the present oxides were found to be spin polarized and are more stable in the ferromagnetic state. This observation is attributed to the p-p interaction between the interstitial atom and the neighboring O atoms. We demonstrate that F-doped oxides are potential p-type ferromagnets, while H-doped are antiferromagnets. The different dopants would induce different magnetic couplings, thus show different ground-state magnetic configurations. The mechanism for the magnetism should be useful for understanding d0magnetic semiconductors or insulators. The present six potential d0ferromagnets and antiferromagnets, at least some of them, may be useful in spintronics.