First-principles Studies On The Spintronics Materials

From the quantum mechanics, we know that the electron has charge and spin properties. Our previous studies mainly focused on the electronic properties of charge, and 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.Computational simulations have the advantage of lower cost and few time compared to artificial experiments. With the continuous improvement of quantum mechanics and solid state theory, and the rapid development of the capability of computers, predicting new functional materials with materials design codes becomes more and more powerful. In this thesis, using the materials design codes of Wien2k and CASTEP, we performed the studies of magnetism and electronic structure on the diluted magnetic semiconductors based on rutile Tio2, the alkaline-earth nitrides and carbides, and the surfaces and interfaces of half-metallic ferromagnets.The studies on diluted magnetic semiconductors based on rutile TiO2 indicate that both V- and Cr-doped rutile TiO2 behavior ferromagnetism, and the Curie temperatures are room-temperature or above it; There is a transition from a half-metal to a semiconductor when taking account of the Coulomb correlation interaction of 3d of Ti, V and Cr for these doping systems; in addition, the oxygen vacancy has large effect on the electronic structure and magnetism of Cr-doped rutile TiO2.For alkaline-earth nitrides, our calculations show that only CaN, SrN and BaN are half-metallic in all the rock-salt MX (M= Ca, Sr, Ba; X= N, P, As), but all the zinc-blende MX behavior half-metallic characteristic. For alkaline-earth carbides, we predict that rock-salt SrC and BaC are half-metallic ferromagnets, or at least the corresponding half-metallic ferromagnetic films can be grown on the semiconductor substrates of PbS and PbSe, respectively. We also predict the possibility of the epitaxial growth of zinc-blende CaC, SrC and BaC half-metallic films on appropriate semiconductor substrates; In addition, above room-temperature Curie temperatures are find for these alkaline-earth carbides, which makes them more promising candidates for the practical applications of spintronics devices.The calculations of the surfaces of zinc-blende CaC (110), (001) and (111) indicate that only the (110) surface and the C-terminate (111) surface maintain the half-metallic ferromagnetism as shown in bulk CaC, which is helpful for the epitaxial growth of zinc-blende CaC half-metallic ferromagnetic films; For the CrTe/ZnTe(001) interface, we find that both the Cr-terminate and Te-terminate CrTe/ZnTe(001) interfaces preserve the half-metallicity as shown in bulk zinc-blende CrTe, but the topmost surfaces lost the half-metallicity.