The mechanism of ferromagnetism stability in sandwich clusters
Vn​(C6​H6​)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
1μB​ to the magnetic moment but little to the magnetic coupling of
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.
Kanamori and K. Terakura, J. Phys. Soc. Jpn. 70, 1433 (2001)]. However, the
presence of edge Bz's in the cluster introduces an important modification. A
simple model is constructed to explain the essence of the physical picture.Comment: 16 pages, 7 figure