Crystallographical and morphological changes in charge-ordering transition of RFe₂O₄ (R: Y, Lu) investigated by transmission electron microscopy

Temperature dependence of charge-ordered crystal structures and domain structures in RFe₂O₄ (R: Y and Lu) was investigated by energy-filtered transmission electron microscopy, combined with conventional transmission electron microscopy. The presence of three-dimensional to two-dimensional charge ordering transition were observed in both YFe₂O₄ and LuFe₂O₄ on heating. Furthermore, real-space images obtained with the energy-filtered transmission electron microscopy revealed that YFe₂O₄ has less anisotropic nanometer-scale charge-ordered domains than LuFe₂O₄. These findings in RFe₂O₄ indicate the importance of the interchange interactions between Fe-O bilayers in addition to those within bilayers in the structural phase transitions associated with charge ordering in this system.