First-Principles Study Of Half-metallic Mn₂ZnSi And MN（M=Mg, Sr, Ba）

In this thesis, two types of half-metal Mn2ZnSi and MN (M=Mg, Sr, Ba) are predicted by first-principle calculation, the magnetic properties and influence of increased pressure for the magnetic moments are also investigated.In the early1980s, Rob de Groot and collaborators discovered a new type of magnetic material:half-metal. The feature of this new type material is two spin channels shows different conductive characteristic, for which one of the two spin channels shows a typical metallic be-havior while the other has semiconductor or insulator properties. At this material with100%spin-polarization, the spin orientation of conduction electrons is in the same direction. For half-metal both has metallic and insulating band properties, is regarded as a new type of functional material. However, many unique natures of half-metal make it has great potential application in random access memory and spintronic. First-principle calculation can theoretically predict half-metal with great application value, thus it can guide the experimental synthesis.At first we gived a short introduction to the development and the basic concept of DFT. Only simple H atom can be calculated by quantum mechanics at the very beginning of its foundation. Several years later, E. A. Hylleraas and D. R. Hartree calculated the ground state of Helium atom by variational and self-consistent field method, respectively; V. Fork improved the self-consistent field method forming the well-know Hartree-Fork method. This method is the prototype of many modern methods for electronic structure calculation, The DFT was founded in1960’s, it is widely used in materials simulations and computational chemistry because of its high precision and moderate computational consumption.In the third chapter, by first-principle calculation, the electronic structure and magnetic properties of the Mn2ZnSi full-Heusler alloy are investigated. Calculations show that Mn_>ZnSi compound presents half-metallic ferrimagnetic properties under the equilibrium lattice constant. The influence of spin-orbit interaction for the magnetic moments is investigated. The result shows spin-orbit interaction has little influence on magnetic moment. The bulk modulus of Mn^ZnSi obtained by a fit of the Murnaghan equation of state is134.3GPa, which is more compressible than some other Heusler alloys. At the pressure range of0to17.7GPa, Mn2ZnSi presents half-metallic character. Mn2ZnSi would be a promising material for future spintronic applications.In the fourth chapter, magnetic properties of sp-electron half-metallic MN (M=Mg, Sr, Ba) in rocksalt structure under pressure have been investigated using density functional theory. The calculated results show that the three compounds are half-metallic ferromagnets at equilibrium state. With the pressure increasing, firstly the half-metallic properties of the three compounds are disappeared, then with the pressure continuously increasing, MgN and BaN will occur pressure-induced magnetic phase transitions from ferromagnetic to nonmagnetic state. These features will be useful for future applications.In the final chapter, we made a conclusion for this thesis, and made a plan for the following work.