LiFe₂Cl_n (n = 4–6) clusters: Double-exchange mediated molecular magnets

A systematic study of LiFe₂Cl_n (n = 4–6) clusters, based on gradient corrected density functional theory (DFT), shows that the electron contributed by Li can transform antiferromagnetic Fe₂Cl_n (n = 4 and 6) clusters into ferromagnetic clusters. In Fe₂Cl₆ (Fe₂Cl₄) cluster, the Fe atoms in +3 (+2) oxidation states are aligned antiferromagnetically, consistent with the super-exchange model. The extra electron from Li atom creates a charge disproportionation in the LiFe₂Cl₆ (LiFe₂Cl₄) cluster that mediates the double-exchange interaction between the Fe atoms. Antiferromagnetic to ferromagnetic transition can also be induced by hole doping as seen to be the case with Fe₂Cl₅ which has a ferromagnetic ground state. Simultaneous electron and hole doping is also seen to impact on the magnetic properties of LiFe₂Cl₅ which can be viewed as (Fe₂Cl₄+LiCl). While Fe₂Cl₄ is antiferromagnetic and LiCl is nonmagnetic, the ground state of LiFe₂Cl₅ is ferromagnetic. We also analyzed the results with on-site Coulomb interaction U by performing DFT+U calculations. These results can be useful in the synthesis of functional molecular magnets.