First-Principles Calculations On Electronic Structure And Magnetism Of Rare Earth Gd/Smiconductors Composites

The magnetic moment of rare earth metals is from the localized 4f electrons. Rare earth metal Gd is one of the four room-temperature ferromagnetic metals with Curie temperature of 293 K. The ferromagnetic order generated by the localized Gd 4f electrons polarizes the 5d and 6s conduction electrons, leading to a large magnetic moment of 7.63 μB/Gd. Composite materials consisted of rare earth metals and semiconductors will have potential applications in spintronic devices.In this dissertation, we study the electronic structure and magnetism of N defect and anion doped half-metal Gd N, rare earth metals doped ZnO and monolayer MoS₂ and the interfaces consisted of Gd（0001） and monolayer MoS₂ by first-principles calculations based on the density functional theory.Firstly, we calculated the electronic structure and magnetism of N defect and anion M（M=B, C, O, F, P, S and As） doped Gd N. It is found that doping of O is the most energy favorable. For O, F, S and N defect doped cases, the Fermi level moves upward, spin polarization decreases and magnetic moment of systems increases slightly; For C and B doped cases, the Fermi level move downward, spin polarization decrease and magnetic moment of systems increase slightly; For P and As doped cases, due to P and As are isovalent to N and heavier than N, the magnetic moment of systems is almost unchanged and the half-metallic character disappears.Secondly, we calculated the electronic structure and magnetism of RE（RE=La, Ce, Pr, Nd and Eu） doped ZnO. It is found that doping of Ce is the most energy favorable. From the spin densities difference, it can be seen that the spin-polarized charge densities of O and Zn atoms near RE are very small, highly localized and limited to the four nearest neighboring O atoms. The ground states of Pr, Nd and Eu dopants at Zn sites are weakly antiferromagnetic but the ground state of Ce dopants is ferromagnetic as the doped RE（RE=Ce, Pr, Nd and Eu） atomic concentration is 12.5%.Also, we calculated the electronic structure and magnetism of Gd-doped monolayer MoS₂. It is found that the different magnetic coupling between the Gd atoms cannot be simply attributed to the distance between two Gd atoms and it is also closely related to the directional nature of electronic structure or chemical bonding of MoS₂. The most stable magnetic configuration is the weak antiferromagnetic state. The ferromagnetic state is metastable. The ferromagnetism is mediated by ferromagnetic coupling between the Gd 5d and Mo 4d states and intra-atomic d-f exchange interaction.Finally, we calculated the electronic structure and magnetism of interfaces consisted of two-, four- and six-layer Gd（0001） and monolayer MoS₂. It is found that a strong chemical bond between them forms, leading to the Fermi energy of MoS₂ shifting upwards into the conduction band. New surface/interface Gd d states appear at the Fermi energy. The strong hybridization between Gd 5d and Mo 4d states leads to net magnetic moments of 0.15 μB/Mo and all Mo magnetic moments order ferromagnetically. Due to the different chemical environments of the surface and interface Gd atoms, Gd f states shift downward. Compared with bulk Gd, the Gd magnetic moments are enhanced at the surface but reduced at the interface.