Magnetic and Dielectric Properties of HoFe₂O₄ and R_1-xR'_xFe₂O₄ (R, R': Rare Earths)

Rare-earth iron oxides of the form RFe₂O₄ (R = Y, Ho–Lu) show a new mechanism of ferroelectricity owing to the charge ordering of Fe ions below ∼330 K. To determine the physical properties of this system, the magnetic and dielectric properties of HoFe₂O₄ and R_1-xR'_xFe₂O₄ were investigated (R, R': rare earths). All the materials showed dielectric constants of ∼1000–10000, as reported for some other RFe₂O₄ oxides. For HoFe₂O₄, magnetic ordering occurred at a temperature lower than those of RFe₂O₄ reported thus far. On the other hand, the dielectric measurements of this material suggested the development of a correlation between polar regions at higher temperatures, which was also observed for the Sc-substituted system Lu_1-xSc_xFe₂O₄. These results encourage detailed investigations of these materials from the viewpoints of both fundamental and applied sciences, and suggest the existence of other new properties of RFe₂O₄.