The Noncollinear Magnetism Of Small Size Alloying Cluster And One Dimensional Atomic Chain

In recent years, many physists carried out a lot of experiments on the low-dimensional magnetic materials, and found several novel phenomena. At the same time, the theorists provided some explanations for these experimental phenomena. This field has attracted much attention because of the importance of basic research and application. The study of non-collinear magnetic clusters and atomic chains is important for designing new nanometer devices and for revealing the nature of the low-dimensional systems. In this dissertation, by using density functional theory, we theoretically investigate some low-demisional systems.In the first chapter, we mainly introduced the research progress of clusters and atomic chains as well as the concepts of the Pierels transition and spin orbital coupling. Finally, we introduced the research purpose and significance of this paper. The second chapter mainly introduces calculation details and the theoretical basis of density functional theory. We also present the major characters of the Vienna ab initio Simulation Packages (VASP) employed here.In the third chapter, using density functional theory, the structures, stabilities and magnetic properties of (FeCr)n (n≤6) alloying clusters were investigated. For smaller clusters with n≤3, the results show that the ground-state system possesses collinear antiferromagnetic order. For n≥4cases, however, the ground state cluster possesses non-collinear magnetic order. Therefore, there is a collinear to non-collinear magnetic transition at n=4in (FeCr)n systems. In addition, although the spin-orbit coupling effect of3d transition metal atom is often weak, the results indicate that the orbital magnetic moments of some certain clusters are significant and important. Finally, the chemical bond of non-collinear magnetic clusters and the physical origin of the magnetic transition were analyzed.In the fourth chapter, using density functional theory and time-dependent density functional theory, we performed theoretical investigations on the structural and optical properties of the CpTMC6o(TM=Sc-Fe) sandwich cluster. The calculated results show that, in the ground-state clusters, the coordination manner of C6o is different. For CpScC6o, CpTiC6o, CpVC6o and CpCrC6o, C60serves as anη6ligand, while it is used as a η5ligand in CpMnC60and CpFeC60-Such a structure transition is caused by bond variation. Furthermore, the optical properties of CpScC60, CpVC6o and CpMnC6o were investigated. The results show that these systems could exhibit high absorption capacities in ultraviolet, visible or near-infrared regions. In the fifth chapter, the structures, stabilities and magnetic properties of4d transition metal monatomic chains were systematically investigated. Although the predicted geometrical parameters and magnetic orders in Zr, Nb, Mo, Tc and Rh zigzag chains could well reproduce existing data, however, the magnetic orders of ground states of Y and Pd zigzag chains are identified as non-collinear magnetic states and Ru chain is identified as antiferromagnetic state. More importantly, there exists a magnetic phase transition that is caused by dimerization in the Ru zigzag chain, and we find the enhanced metallic bond is the physical origin of the non-collinear magnetic chains.In addition, in some cases such as Tc, Ru and Rh chains, the contribution of orbital magnetic moments is large and could not be neglected. Specially, for the two non-collinear magnetic systems, the orbital magnetic moments are much larger, indicating there exists a strong spin-orbit coupling interaction in these systems.In the sixth chapter, the structures, stabilities and magnetic properties of3d and5d transition metal monatomic chains were systematically investigated. The calculated results show that their ground states are also zigzag types, and the ground states with dimerization were not found in3d and5d chains. For3d chains, with the increase of atomic number, the ground state changes from ferromagnetic to antiferromagnetic and finally to ferromagnetic order. Further investigation show that magnetic transition arised from enhanced covalent bond. Finally, we found that the orbital magnetic moment was very small and could be neglected in3d systems. However, for5d systems, the orbital magnetic moment are very large, which represents a strong spin-orbit coupling interaction in these systems.