Theoretical Research On The Magnetic Structure-activity Relationship Of Single-molecule Magnets

As an emerging field of science,single-molecule magnets(SMMs)are interdisciplinary in physics,chemistry,materials science,life sciences and medicine.In recent years,single-molecule magnets have become the hot topic in research.Ever since the birth of the first single molecule magnet,scientists have discovered its amazing application prospects.The current storage technology is cobalt-platinum alloy,with one bit stored in hundreds of particles and 6-7 nm in size.For single molecule magnets,they show the magnetic hysteresis and slow relaxation behavior,with an energy barrier between two opposite directions of magnetization,resulting in that it can provide relatively stable binary.Scientists expect that the stored density of single-molecule magnets can be up to 220 TBit/in2! However,the problems faced by technology based on monomolecular magnets are also severe,mainly involving two aspects:(1)the characteristics of single molecule magnets can only be obtained at liquid-helium temperatures;(2)there are few examples of depositing and addressing on the surfaces of single molecule magnets.Therefore,it is urgent to design an effective single molecule magnet.The main criterion for determining whether a single molecule magnet is effective is its blocking temperature,which is affected by the effective energy barrier(Ueff,also known as anisotropic barrier).Aiming at this problem,this paper studies the intrinsic relationship between the effective energy barrier and their structures of a series of SMMs.Firstly,the exploration is the influence of the pentamethylcyclopentadienyll-ligand environment in SMMs based on lanthanide Dy.It is found that,for oblate ion-based SMMs,the length of coordinate bonds on the equatorial plane impeded the performance of SMMs.For the influence of axial crystal field,the more centripetal the crystal field is,such as bis-pentamethylcyclopentadienyl ligands,the higher the magnetization inversion barriers can be.In addition,when the bis-pentamethylcyclopentadienyl ligands are along the axial,the closer the coordinate atoms are to the axial direction,the higher magnetization reversal barriers can be.Then,we explored the influence of the crystal field with pentagonal bipyramidal symmetry in magnetic anisotropy of lanthanide metal magnets.It is found that SMMs based on Dy3+ metal ions can obtain high performance with the pentagonal-bipyramidal-symmetry crystal field.However,for oblate ion-based SMMs,if the main magnetic axis of ground Kramers doublets state is located on the equatorial plane,they will show weak magnetic behavior;at the same time,the weak ligand field along the axial is beneficial to design high-performance SMMs.When the main magnetic axis of the ground state is along the axis orientation,the strong ligand field strength along the axial orientation is conducive to its becoming a high quality single molecular magnet.