Magnetic and dielectric properties of InFe₂O₄, InFeCuO₄, and InGaCuO₄

The magnetic and dielectric properties of InFe₂O₄, InFeCuO₄, and InGaCuO₄ have been investigated. All these materials are isostructural with RFe₂O₄ (R = Y, Ho-Lu), which shows ferroelectricity due to iron-valence ordering. InFe ₂O₄ exhibits ferrimagnetic ordering at T_c ∼ 242 K and a dielectric constant (ε) of ∼10000 at around room temperature. These properties resemble those of RFe₂O₄; the origins of the magnetic and dielectric phenomena are likely common in InFe₂O₄ and RFe₂O₄. From measurements of the other two materials, we found that both T_c and ε are decreased in the order of InFe₂O₄, InFeCuO ₄, and InGaCuO₄. This result strongly supports the previously reported explanation based on an electron transfer between the Fe-site ions for the corresponding rare-earth systems. Therefore, we propose that the dielectric properties of the oxides isostructural with AFe ₂O₄ are plausibly governed by electron transfer; this situation is different from that of ordinary ferroelectrics and dielectrics, in which the displacement of cations and anions is important. In addition, InFeCuO₄ and InGaCuO₄ exhibit large ε values (δ > ∼1500). In consideration of this property, we discuss the possible applications of these oxides.