First-principle Studies The Property Of The Diluted Magnetic Semiconductors Doped With Ca,Ti,C And The Binuclear Manganese Molecular Magnet

In this thesis, using the full potential linearized augmented plane wave (FP-LAPW) method, we studied the electronic structure and properties for the intrinsic non-magnetic elements doped semiconductors, such as, calcium-doped gallium nitride, titanium-doped aluminum nitride and carbon-doped zinc sulfide; and the electronic structure and magnetic properties for the binuclear manganese molecular magnet Mn2(dpp)2(H2O)2Cl4]·2H2O, dpp=2,3-bis (2-paridyl) pyrazine.Diluted magnetic semiconductors (DMSs) have attracted considerable attentions for their potential applications in spintronics. During the past decade, a number of transition metals doped DMSs with above room temperature ferromagnetism have been reported. However, there is still no consensus regarding ferromagnetism originates from a uniform alloy or from secondary phases. Therefore, it has been focus to study the intrinsic non-magnetic elements doped diluted magnetic semiconductors. Compared to the traditional inorganic magnetic material, molecule-based magnets hold some properties, such as, low density, transparency, low-temperature fabrication and electrical insulation etc. Molecule-based magnets also attract many researchers' interests. Hence, it is more significant to investigate the magnetic exchange mechanism and electronic structure for the molecule-based magnetic materials.Based on our calculations, we find the intrinsic non-magnetic elements Ca, Ti and C can order ferromagnetism in some semiconductors such as GaN, AlN and ZnS. Compared to the traditional transition metal elements doped diluted magnetic semiconductors, the intrinsic nonmagnetic elements doped diluted magnetic semiconductors have some merits, higher solid solubility, forming shallower impurity levels, and avoiding the secondary ferromagnetic phases. These results indicate the diluted magnetic semiconductors doped with the intrinsic non-magnetic elements would be widely used in spintronics. Our studies would guide the diluted magnetic semiconductor fabrication.The calculations reveal that the compound [Mn2(dpp)2(H2O)2Cl4]·2H2O,dpp=2,3-bis (2-pyridyl) pyrazine has stable ferromagnetic ground state. There exists a dominant intra-molecule ferromagnetic interaction through the double chloro-bridge between Mn2+ ions. Mn2+ and its coordination atoms form sp3d2 hybridization. Mn2+ 3d-electrons form high spin distribution. The total density of states shows this compound is a semiconductor. The obtained results indicate double chloro-bridge two Mn2+ ions with octahedron structure is good candidates for synthesizing molecular based ferromagnets.