Molecular polarons and valence fluctuations in Fe3O4

Abstract

We propose a ‘molecular polaron’ model which describes the properties of valance fluctuations in Fe₃O₄ above the Verwey transition temperature. The molecular polaron is dynamically coupled cluster, or a vibronic state associated with two electrons in four-site molecular orbitals coupled to local vibrational modes with T_2g symmetry. The lifetime of a molecular polaron is assumed to be long enough to induce a strain field around it. That is, each molecular polaron is considered to be ‘dressed’ by an instantaneous strain field. Based on this model, neutron Huang scattering due to the strain field around independent molecular polarons has been calculated. The observed patterns of neutron diffuse scatteringagree quite well with the calculated patterns, which seems to ensure the validity of the proposed model.