Tight-binding model of Mn-12 single-molecule magnets: Electronic and magnetic structure and transport properties

Article

关键词: ORBIT-COUPLING CONSTANTS;    TRANSITION-METAL IONS;    HIGH-SPIN MOLECULES;    RELAXATION;    MANGANESE;    SPECTRA;    ATOMS;    SUSCEPTIBILITY;    ANISOTROPY;    CRYSTALS;   

DOI  :  10.1103/PhysRevB.85.245415

来源: SCIE

【 摘 要 】

We describe and analyze a tight-binding model of single-molecule magnets (SMMs) that captures both the spin and spatial aspects of the SMM electronic structure. The model generalizes extended Huckel theory to include the effects of spin polarization and spin-orbit coupling. For neutral and negatively charged Mn-12 SMMs with acetate or benzoate ligands, the model yields the total SMM spin, the spins of the individual Mn ions, the magnetic easy axis orientation, the size of the magnetic anisotropy barrier, and the size of the highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO-LUMO) gap consistent with experiment. For neutral molecules, the predicted spins and spatial locations of the HOMO are consistent with the results of density functional calculations. For the total spin and location of the LUMO, density functional theory based calculations yield varied results, while the present model yields results consistent with experiments on negatively charged molecules. For Mn-12 SMMs with thiolate-and methylsulphide-terminated benzoate ligands (Mn-12-Ph-Th), we find the HOMO to be located on the magnetic core of the molecule, but (unlike for the Mn-12 SMMs that have previously been studied theoretically) we predict the LUMO and near-LUMO orbitals of Mn-12-Ph-Th to be located on ligands. Therefore, we predict that for these Mn12 SMMs, resonant and off-resonant coherent transport via near-LUMO orbitals, not subject to Coulomb blockade, should occur. We propose that this effect can be used to identify specific experimentally realized SMM transistors in which the easy axis and magnetic moment are approximately parallel to the direction of the current flow. We also predict effective spin filtering by these SMMs to occur at low bias whether the transport is mediated by the HOMO that is on the magnetic core of the SMM or by near-LUMO orbitals located on the nominally nonmagnetic ligands.

【 授权许可】

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