Study of the Low-Temperature Transition in Magnetite and the Internal Fields Acting on Iron Nuclei in Some Spinel Ferrites, Using Mössbauer Absorption

Abstract

A study has been made of the internal fields acting on ${\mathrm{Fe}}^{57}$ nuclei in some spinel ferrites, with particular reference to the low-temperature order-disorder transition in magnetite, using the techniques of M\"ossbauer absorption. For the ${\mathrm{Fe}}^{3+}$ ions at both the octahedral and tetrahedral sites in nickel ferrite (Ni${\mathrm{Fe}}_{2}$${\mathrm{O}}_{4}$) at 300\ifmmode^\circ\else\textdegree\fi{}K, $\ensuremath{\gamma}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$ at 85\ifmmode^\circ\else\textdegree\fi{} and 300\ifmmode^\circ\else\textdegree\fi{}K, and magnetite (${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$) at 85\ifmmode^\circ\else\textdegree\fi{}K, the effective magnetic field at the ${\mathrm{Fe}}^{57}$ nuclei is the same and equal to about 5.1\ifmmode\times\else\texttimes\fi{}${10}^{5}$ oe. In magnetite, the value of ${H}_{\mathrm{eff}}$ in the ${\mathrm{Fe}}^{2+}$ ions is about 4.5\ifmmode\times\else\texttimes\fi{}${10}^{5}$ oe at 85\ifmmode^\circ\else\textdegree\fi{}K. Measurements on ${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$ 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.