EXAFS spectroscopic analysis of the Verwey transition in Fe3O4

We present an extended x-ray absorption fine structure study at the Fe K edge of the local structural changes in Fe3O4 across the Verwey transition at TV∼120 K. The local structure of the FeO6 octahedra is distorted below TV and remains unaltered during the transition, the local distortions being already present in the pseudocubic phase above TV. The phonon modes responsible for the lattice distortion are those associated with displacements of the octahedral Fe-Fe chains. We propose that the metal-insulator transition is then caused by a change in the regime of the local distortions from a static regime at low temperatures to a dynamical one at high temperatures, the lattice dynamics above TV being the origin for the electrical conductivity