Magnetic property and charge ordering effect in polycrystalline LuFe2O4

Abstract

The charge ordering effect in LuFe2O4 powder is investigated with the vibrating sample magnetometer and Mössbauer spectroscopy. The crystal structure of LuFe2O4 shows the two-dimensional layered type rhombohedral(R3¯m) structure. The lattice constants are found to be a0=3.439Å and c0=25.258Å by the Rietveld refinement. The Néel temperature (TN) is determined to be 250K. The Mössbauer spectra consist of four sextets indicating the magnetic ordering below TN, where three sets are assumed to be Fe3+ phases and the other is Fe2+ at 4.2K, and two doublets splitting in a paramagnetic region. At room temperature, the electric quadrupole splittings (ΔEQ) of two doublets are 0.22±0.01 and 0.67±0.01mm∕s, respectively. The isomer shift value of a doublet with smaller ΔEQ is 0.18±0.01mm∕s relative to the Fe metal, which is consistent with the Fe3+ valence state, while the value of a doublet with larger ΔEQ is 0.83±0.01mm∕s indicating Fe2+ state. The Mössbauer spectra suggest that the observed asymmetry below 370K is due to the charge ordering effect between Fe2+ and Fe3.