Theoretical Study On Magnetic Anisotropy Of Rare Earth Single-molecule Magnets

Molecular magnetic materials, as an important discover since 90s, have great potential application in future. Molecular magnetic materials are significant both in theory and practice due to their excellent magnetic properties. Firstly, on the theoretical side, these magnetic materials which have slow magnetic relaxation and quantum tunneling effect can be used to study mechanism of the transformation between quantum mechanics and classical mechanics. Secondly, on the practical application side, we can use molecular materials for date storage. As their storage unit is only a single molecule, their storage density will be greatly improved. We hope to make high density date storage devices using single-molecule magnets (SMMs) which can be used in quantum computing. But unfortunately, the blocking temperatures TB of molecular magnetic materials are all far below room temperature, and so there is a long way for us to put them into practical applications. Therefore, in order to obtain single molecular magnetic materials which have high blocking temperature, we should find the relationships between blocking temperature and molecular structure ?element composition. We hope our work will promote the molecular magnetic materials into practical application early.Firstly, we investigated the magneto-structural correlations of single molecule magnets which has one Dy magnetic center with different coordination environment.We investigated the influence of molecule structures on magnetic anisotropy. We summarized the frequent causes to affect the energy barrier of Dy-based SMMs: the axial symmetry of molecule structure, charge distribution around the center magnetic-ion, the quantum tunneling gaps, et al. We found that the higher axial symmetric structure and the more negative charge distribution along the axial orientation will be benefit for SMMs with high performance.Secondly,we investigated complex [Dy(?-OH)(DBP)2(THF)]2 which has two magnetic center ions. Compound has five coordination numbers, and two Dy ions are linked by five cyanide. From the calculated results using CASSCF/RASSI method,we found that compound has a large energy barrier, and the Dy-Dy interaction is antiferromagnetic. Moreover, we found that the calculated energy levels with CAS(11,8) will be closer to experiment compared with CAS(9, 7). Thus, it is reasonable for us to use larger active space for SMMs with strong crystal field to take into account electrons from atoms around Dy in CASSCF calculation.