Doping effect on charge ordered structure in RFe2O4 (R=Lu and Yb)

Doping effects on the charge ordered (CO) structure in RFe2O4 (R=Lu, Yb) were investigated by an energy-filtered transmission electron microscope (EF-TEM), in combination with conventional magnetic measurement. The repalcement of Cu2+ and Co2+ for Fe2+ in RFe2O4 (R=Lu, Yb) destroyed drastically the CO structure. In LuFeCuO4, the CO structure with q=1/3 1/3 1/2 disappear and short-ranged domains consisting of cationic ordering of Fe3+ and Cu2+ ions are formed, which gives rise to characteristic zigzag-shaped diffuse streaks with diffuse spots at the h/3-δ h/3-δ 0-type positions (h: integer, δ=0.06) in reciprocal space. In addition, the magnetic measurement revealed that LuFeCuO4 exhibits a magnetic transition around 50K, which is much lower than the Neel temperature of 250K in LuFe2O4. In YbFeCoO4, clusters consisting of Fe3+ and Co2+ in the triangular lattice are formed and give rise to honeycomb-shaped diffuse streaks.