Abstract
The mechanism of ferromagnetism stability in sandwich clusters Vn(C6H6)n+1 has been studied by first-principles calculation and model analysis. It is found that each of the three types of bonds between V and benzene (Bz) plays different roles. V 3dz2 orbital, extending along the molecular axis, is weakly hybridized with Bz’s HOMO−1 orbital to form the σ-bond. It is quite localized and singly occupied, which contributes 1 μB to the magnetic moment but little to the magnetic coupling between neighboring V magnetic moments. The in-plane dx2−y2, dxy orbitals are hybridized with the LUMO of Bz and constitute the δ-bond. This hybridization is medium and crucial to the magnetic coupling though the δ states have no net contribution to the total magnetic moment. dxz, dyz, and HOMO of Bz form a quite strong π-bond to hold the molecular structure but they are inactive in magnetism because their energy levels are far away from the Fermi level. Based on the results of first-principles calculation, we point out that the ferromagnetism stability is closely related with the mechanism proposed by Kanamori and Terakura [J. Phys. Soc. Jpn. 70 (2001) 1433]. However, the presence of edge Bzs in the cluster introduces an important modification and suppresses significantly the ferromagnetism stability. A simple model is constructed to explain the essence of the physical picture.
