Synthesis and magnetic-electronic characterization of mixed-valence LuFe2O4-δ: effect of stoichiometry δ

Samples of LuFe2O4-delta of varying oxygen stoichiometry (delta), prepared by solid state synthesis, have been characterised by x-ray diffraction, Fe-57 Mossbauer-effect spectroscopy, SQUID magnetometry and transmission electron spectroscopy as well as electron-diffraction analysis. Magnetisation measurements show that the onset of ferrimagnetic ordering is confined to 245-250 K for the synthesised samples. Detailed analysis of Mossbauer spectra measured at variable cryogenic temperature confirm the mixed valence state and reveal the effects of charge and spin frustration of the triangular network of Fe atoms. The electron diffraction analysis demonstrates the existence of charge ordered superstructure (satellites) as well as an inhomogeneous distribution of oxygen throughout the lattice, irrespective of the delta values.