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Abstract: We have investigated the magnetic and dielectric properties of YbFe2− x Mn x O4 (0⩽x⩽1), which is an Fe-site-substituted system of new multiferroic oxides RFe2O4 (R=Y, Ho–Lu). X-ray diffraction measurements show that a solid solution is formed between YbFe2O4 (x=0) and YbFeMnO4 (x=1) for 0⩽x⩽1, whereas only compounds with x=1 (i.e., RM 1 M 2O4; M 1 and M 2=trivalent and divalent cations, respectively) have been known for the Fe-site substitution in RFe2O4. The valence of the Mn ion is determined to be ∼2+, consistently with the suppression of low-temperature magnetization by the Mn substitution. The magnetic transition temperature (T N) and the dielectric constant (ε′) decrease monotonically with increasing x. This result plausibly confirms that the magnetic and dielectric properties in oxides isostructural with RFe2O4 are governed by the electron transfer between Fe-site ions, unlike ordinary ferroelectrics and dielectrics, in which the ionic displacement plays a key role. The possibility for application is briefly discussed as well. [Copyright &y& Elsevier]

The magnetic and dielectric properties of perovskite manganites R0.5Ca0.5MnO3 (R = Eu-Lu), which show charge ordering of the Mn-3d electrons below room temperature, have been investigated. Their dielectric constants were ∼ 1000-10000 at around room temperature. Inflections or peaks of temperature dependences of the dielectric constants were observed at around the charge-ordering temperatures. Analyses of tan δ for R = Eu-Lu and EXAFS spectra for R = Dy suggested that the dielectric properties of the present system are rooted in a special arrangement and transfer of the Mn-3d electrons. The two-peak structure of tan δ indicates that dielectric measurement can be used to observe homogeneity or inhomogeneity of sample, as mentioned in our previous paper on the ruthenium perovskite oxides. [ABSTRACT FROM AUTHOR]

We report dielectric and magnetic properties of a single crystal of LuFe2O4 with different degrees of oxygen deficiency. The oxygen stoichiometry was monitored with the gas mixture ratio of CO2 and CO during the crystal growing process. A sample having high resistivity of about 10 kΩ cm sample was found at room temperature. The relation between the control of the charge frustration and the completeness of the charge ordering is discussed. [ABSTRACT FROM AUTHOR]

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. InFe2O4 exhibits ferrimagnetic ordering at Tc ~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 Tc and e are decreased in the order of RFe2O4, RFeCuO4, and RGaCuO4. 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 RFe2O4 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, RFeCuO4 and RGaCuO4 exhibit large ϵ values (ϵ >~1500). In consideration of this property, we discuss the possible applications of these oxides. [ABSTRACT FROM AUTHOR]