Magnetic property and charge ordering effect in polycrystalline LuFe2O4

The charge ordering effect in LuFe2O4 powder is investigated with the vibrating sample magnetometer and Mossbauer spectroscopy. The crystal structure of LuFe2O4 shows the two-dimensional layered type rhombohedral(R (3) over barm) structure. The lattice constants are found to be a(0)=3.439 A and c(0)=25.258 A by the Rietveld refinement. The Neel temperature (T-N) is determined to be 250 K. The Mossbauer spectra consist of four sextets indicating the magnetic ordering below T-N, where three sets are assumed to be Fe3+ phases and the other is Fe2+ at 4.2 K, and two doublets splitting in a paramagnetic region. At room temperature, the electric quadrupole splittings (Delta E-Q) of two doublets are 0.22 +/- 0.01 and 0.67 +/- 0.01 mm/s, respectively. The isomer shift value of a doublet with smaller Delta E-Q is 0.18 +/- 0.01 mm/s relative to the Fe metal, which is consistent with the Fe3+ valence state, while the value of a doublet with larger Delta E-Q is 0.83 +/- 0.01 mm/s indicating Fe2+ state. The Mossbauer spectra suggest that the observed asymmetry below 370 K is due to the charge ordering effect between Fe2+ and Fe-3.