Electron states of iron atoms and hyperfine interaction parameters in the low temperature phase of magnetite

Computer processing of Fe3O4 Mössbauer spectra with subsequent processing by Karyagin’s method provides a new interpretation of the spectra of the low-temperature phase of magnetite. The Fe3O4 spectrum at T = 80°K is described well by seven sets of lines in two of which forbidden transitions were observed, related to the large value of the quadrupole interaction and the highly nonaxial local field. Electronic configurations and effective charges of the iron atoms are determined from the values of isomer shifts and effective magnetic fields of the nuclei in magnetite below the Verwey transition temperature. The significant difference in hyperfine parameters of “bivalent” ions at octahedral sites below the phase transition is explained by formation of covalent pairs of these ions. Spectral components characteristic of the low-temperature phase of magnetite were observed in the spectrum of stoichiometric magnetite at a temperature approximately 4°K above the phase transition point. Evidently charge ordering (or local lattice distortion) begins somewhat sooner than the phase transition as determined by the point of the temperature discontinuity in electrical conductivity.