Theoretical Study Of Charge-induced High Spin State In Diradical Organic Molecules

Based on the Kondo-Peierls-Hubbard model,we have theoretically studied some properties of charge-induced high spin state in diradieal organic molecular magnets, by using the exact diagonalization technique.1.The effects of charge delocalization on the magnetic properties of diradieal organic molecules.After considering the charge deloealization of the radicals,it is found that when the radicals tend to be singly occupied and the spin correlation between the radical and its nearest-neighboring site is positive,the system can be in a high spin state.At this time,the two side radicals have a ferromagnetic spin correlation,and the spins between the radical and main-chain are also ferromagnetically coupled.The magnetic properties of the system depend on the hopping integral(t_R ) and the radical Coulomb repulsion energy(U_R ).Electrons can transfer between radicals and the main-chain due to the hopping integral.Further more under the effect of the main-chain coulomb repulsion energy,electrons will transfer from the main-chain to the radicals.With the t_R increasing,the radicals tend to be doubly occupied.Therefore,larger hopping integral is not preferable for the system to be in a high spin state.While the radical coulomb repulsion energy can baffle this hopping,and this effect becomes stronger with the increase of U_R.As a result,the radicals prefer to be singly occupied.Thus,stronger coulomb repulsion energy is preferable for the system to be in a high spin state.2.The effects of inter-chain coupling on the magnetic properties of diradical organic molecules.After considering the inter-chain coupling,the system presents a high spin state when the doped charge is distributed between the two chains.At the moment,there is a ferromagnetic spin correlation between any couple of the radicals, and the spins between the radical and the main-chain is also ferromagnetically coupled.The magnetic properties of the system depend on the strength of the inter-chain coupling(t_L) and the main-chain coulomb repulsion energy(U).The value of t_L for a high spin state increases with increasing U.Electrons can jump between the two chains due to the existence of inter-chain coupling,and the jump becomes easier as the increase of t_L,which makes the doped charge distribute between the two chains.Thus,larger inter-chain coupling is preferable for the system to be in a high spin state.However,the main-chain Coulomb repulsion energy U will make the doped charge distribute mainly in one chain of the system,leading to a very weak inter-chain spin correlation.Therefore,stronger main-chain coulomb repulsion energy is not preferable for the system to be in a high spin state.