Verwey transition in magnetite: Mean‐field solution of the three‐band model
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The nature of the Verwey transition in magnetite (FqO,) within a three-band spinless model Hamiltonian is examined. These bands, which arise from the minority-spin tZg orbitals on the Fe(B) sublattice, are occupied by half an electron per Fe(B) atom. The Verwey order-disorder transition is studied as a function of the ratio of the intersite Coulomb repulsion Ur and the bandwidth W. It is found that the electrons are ordered beyond the critical value of U,lW=O.25 in essential agreement with the results of the one-band Cullen-Callen model. For larger values of lJ,JW, a Venvey-like order is exhibited where the electrons occupy alternate (001) planes. The model predicts a transition from the metallic to the semiconducting state with the band gap increasing linearly with U, beyond the transition point.