A Theoretical Study Of The Magnetic Properties Of Molecular Magnets

Molecule magnets are magnetic units at the molecular level.They have some advantages of high storage density,diversified structures and easy processing.Therefore,they have potential to be used as,for instance,high-density data storage devices,spintronics,quantum computation etc.Some theoreties of density functional theory(DFT),complete active space self-consistent filed(CASSCF)etc and experiment were employed to probe the magnetic properties of a series of single-ion magnets(SIMs)and single-chain magnets(SCMs).(1)Why the SIMs composed by “prolate” lanthanide ion Er^? cannot possess energy barriers as high as Dy^??According to the proposal by Long etc.,equatorially-coordinated ligand environments are preferable to“prolate”lanthanide ions such as Er^? to have large energy barriers.However,our calculations show that the larger g_x,y values in the first excited Kramers doublets(KDs)induced by the surrounding equatorially-coordinated ligands lead to their larger transversal magnetic moments so as to fast quantum tunneling of magnetizations(QTMs)in their first excited states.And so,the spin-phonon transitions can only proceed from the ground to the first excited KDs for our studied three compounds and all models.On the other hand,the effective energy barriers U_eff of three compounds are smaller than the calculated energy gaps between the lowest two KDs due to their more flexible molecular structures.For the above reason,the energy barriers didn't increase continuously as we expected when we decreased the Er-L bond lengths.We deduced that mononuclear Er^? compounds cannot easily possess huge energy barriers through enhancing the surrounding equatorially-coordinated ligand field.(2)DFT and ab initio calculations were performed to probe the origin of magnetic relaxation barriers of two finite SCMs featuring one-dimension chain.Our calculations show that the strong intra-chain Co^?-Co^? exchange coupling interactions transmitted by radicals can contribute much more than ionic anisotropy to the height of the reversal barrier of magnetization for the SCMs with|2E|<|4J/3|.In addition,the anisotropic energy barrier?_A decrease with the consistent decrease of|2E/J|ratio and finally vanish in the limit of broad domain walls(DWs)(|2E|<<|4J/3|).Therefore,the total magnetic relaxation energy barrier of two SCMs mostly originate from the correlation energy barrier??deriving from the indirect ferromagnetic interaction between Co^?-Co^? transmitted by the strong antiferromagnetic alternating arrangement of Co^? and radicals.