Study of the low-temperature transition in magnetite and the internal fields acting on iron nuclei in some spinel ferrites, using Mössbauer absorption

A study has been made of the internal fields acting on Fe57 nuclei in some spinel ferrites, with particular reference to the low-temperature order-disorder transition in magnetite, using the techniques of Mössbauer absorption. For the Fe3+ ions at both the octahedral and tetrahedral sites in nickel ferrite (NiFe2O4) at 300°K, γFe2O3 at 85°and 300°K, and magnetite (Fe3O4) at 85°K, the effective magnetic field at the Fe57 nuclei is the same and equal to about 5.1×105 oe. In magnetite, the value of Heff in the Fe2+ ions is about 4.5×105 oe at 85°K. Measurements on Fe3O4 at room temperatures provide a microscopic confirmation of Verwey's hypothesis that above the transition temperature of magnetite there is a fast exchange between the ferrous and ferric ions in the octahedral sites.