High-order double exchange in mixed-valence [Fe(III)Fe(II)] cluster

The energy spectrum of the mixed-valence [Fe2+Fe3+] cluster is considered in the model with non-zero overlap of d-functions. The overlap integrals between the states of different localizations are spin dependent: [Psi(ab) . (S)Psi(a).(b)(S)] = -[(S + 1/2)/(2s(0) + 1)]delta(u). Accounting for the non-zero overlap of d-functions leads to a new effect of the double exchange of high-order rank and the essential redetermination of the double exchange and the Heisenberg exchange parameters. It is shown that the high-order double exchange terms change the resonance splittings determined by the classical Anderson-Hasegawa rules. The high-order double exchange contributions to the energy spectrum of the mixed-valence [Fe2+Fe3+] dimer are characterized by the exchange-transfer spin dependence. The parameters tau of the high-order double exchange are the values of the order of magnitude of the Heisenberg exchange parameters, J. (C) 1999 Elsevier Science B.V. All rights reserved.