Abstract
Specific heat measurements of Fe3O4–xFx, obtained using avery sensitive calorimeter, are presented and compared with previous measurements relative to substituated magnetites. We believe that we have been able to detect new phenomena because of the high sensitivity of the apparatus and of the type of substitution. Our results support the following hypothesis: the low-temperature specific heat anomaly, which is associated with a crystallographic symmetry lowering, is due to the presence of octahedral Fe2+ ions which is of particular importance. Furthermore, we propose a new interpretation of the Verwey transition which takes into account recent determinations of the electronic structure of Fe3O4.