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Journal Articles

Magneto-electric effect in charge-ordered LuFe$$_{2}$$O$$_{4}$$

Kambe, Takashi*; Komatsu, Takuma*; Michiuchi, Takamasa*; Hayakawa, Hiroki*; Oishi, Daisuke*; Hanasaki, Noriaki*; Yoshii, Kenji; Ikeda, Naoshi*

Journal of Physics; Conference Series, 200, p.012077_1 - 012077_4, 2010/02

 Times Cited Count:4 Percentile:83.16

A magneto-electric effect (ME) was observed in a charge-ordered ferroelectric LuFe$$_{2}$$O$$_{4}$$. The dielectric response in a three-dimensional charge-ordered phase is strongly influenced by magnetic field, especially around the ferri-magnetic ordering temperature. We also show the relation between the oxygen stoichiometry and the ME signal character above the magnetic transition temperature.

Journal Articles

Magnetic and dielectric properties of YbFe$$_{2-x}$$Mn$$_{x}$$O$$_{4}$$ (0$$underline{<}$$x$$underline{<}$$1)

Yoshii, Kenji; Ikeda, Naoshi*; Michiuchi, Takamasa*; Yokota, Yusuke*; Okajima, Yuka; Yoneda, Yasuhiro; Matsuo, Yoji*; Horibe, Yoichi*; Mori, Shigeo*

Journal of Solid State Chemistry, 182(7), p.1611 - 1618, 2009/06

 Times Cited Count:12 Percentile:46.6(Chemistry, Inorganic & Nuclear)

We have investigated the magnetic and dielectric properties of YbFe$$_{2-x}$$Mn$$_{x}$$O$$_{4}$$ (0$$underline{<}$$x$$underline{<}$$1), which is an Fe-site-substituted system of new multiferroic oxides RFe$$_{2}$$O$$_{4}$$ (R=Y, Ho-Lu). X-ray diffraction measurements show that a solid solution is formed between YbFe$$_{2}$$O$$_{4}$$ (x=0) and YbFeMnO$$_{4}$$ (x=1) for 0$$underline{<}$$x$$underline{<}$$1. The valence of the Mn ion is determined to be $$sim$$2+, consistently with the suppression of low-temperature magnetization by the Mn substitution. The magnetic transition temperature and the dielectric constant decrease monotonically with increasing x. This result plausibly confirms that the magnetic and dielectric properties in oxides isostructural with RFe$$_{2}$$O$$_{4}$$ 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.

Journal Articles

Local structure modulation in the electronic ferroelectric oxide LuFe$$_{2}$$O$$_{4}$$

Hayakawa, Hironori*; Morimoto, Masanori*; Ikeda, Naoshi*; Yoneda, Yasuhiro; Kohara, Shinji*; Yoshii, Kenji; Matsuo, Yoji*; Michiuchi, Takamasa*; Mori, Shigeo*

Transactions of the Materials Research Society of Japan, 34(1), p.51 - 54, 2009/05

We have recently reported that LuFe$$_{2}$$O$$_{4}$$ becomes ferroelectric below 330 K, owing to a charge-ordering transition of Fe ions. As details of the properties of this material have not been reported so far, we have investigated its local structure in the ferromagnetic phase by means of synchrotron X-ray diffraction. The analysis of pair-distribution function showed the existence of displacement of Lu atoms; this structure is different from the average structure of this materials known thus far. This result encourages a detailed reinvestigation of crystal structure of LuFe$$_{2}$$O$$_{4}$$. We also show the results obtained from some other experimental methods, such as dielectric measurement and electron diffraction.

Journal Articles

Stoichiometric study of the dielectric and magnetic properties in charge frustrated system LuFe$$_{2}$$O$$_{4}$$

Michiuchi, Takamasa*; Yokota, Yusuke*; Komatsu, Takuma*; Hayakawa, Hironori*; Kuroda, Tomoko*; Maeda, Daisuke*; Matsuo, Yoji*; Mori, Shigeo*; Yoshii, Kenji; Hanasaki, Noriaki*; et al.

Ferroelectrics, 378(1), p.175 - 180, 2009/00

 Times Cited Count:18 Percentile:62.21(Materials Science, Multidisciplinary)

We have synthesized the samples of LuFe$$_{2}$$O$$_{4}$$, which shows the ferroelectricity due to charge ordering of Fe ions, under several different reducing conditions using a CO$$_{2}$$-CO flow. The reducing condition was changed by changing a flow ratio of CO$$_{2}$$ and CO. It was found that the flow ratio of CO$$_{2}$$/CO of about 5 provided the sample with the highest magnetic transition temperature of 240-250 K. This sample showed the dielectric constant of 10000 at room temperature. The imaginary part of the dielectric response offered the activation energy of 0.4-0.5 eV, which is slightly larger than that reported previously (about 0.3 eV). We will perform further investigation of the physical properties of this sample to clarify full details and their origin of LuFe$$_{2}$$O$$_{4}$$.

Journal Articles

Magnetic and dielectric properties of HoFe$$_{2}$$O$$_{4}$$ and R$$_{1-x}$$R'$$_{x}$$Fe$$_{2}$$O$$_{4}$$ (R, R': rare earths)

Yoshii, Kenji; Yoneda, Yasuhiro; Maeda, Daisuke*; Yokota, Yusuke*; Michiuchi, Takamasa*; Komatsu, Takuma*; Ikeda, Naoshi*; Matsuo, Yoji*; Mori, Shigeo*

Japanese Journal of Applied Physics, 47(9), p.7599 - 7602, 2008/09

 Times Cited Count:8 Percentile:35.16(Physics, Applied)

We have investigated the physical properties of HoFe$$_{2}$$O$$_{4}$$ and R$$_{1-x}$$R'$$_{x}$$Fe$$_{2}$$O$$_{4}$$ (R, R': rare earths). Dielectric measurements showed their dielectric constants of 1000 at around room temperature, which is characteristic of the RFe$$_{2}$$O$$_{4}$$ series (R: rare earths). However, the magnetic transition temperatures and the coherency in dielectric response were found to be different from those of RFe$$_{2}$$O$$_{4}$$ reported so far. Interestingly, these materials suggested higher ferroelectric temperatures than those reported so far, suggesting a possibility of application of these materials.

Oral presentation

Fe 3p-$$>$$1s X-ray resonant emission spectroscopy of LuFe$$_{2}$$O$$_{4}$$ single crystal

Agui, Akane; Mizumaki, Masaichiro*; Kawamura, Naomi*; Kuroda, Tomoko*; Hayakawa, Hironori*; Maeda, Daisuke*; Michiuchi, Takamasa*; Ikeda, Naoshi*

no journal, , 

no abstracts in English

Oral presentation

Magnetocapacitance of electronic ferroelectric LuFe$$_{2}$$O$$_{4}$$

Komatsu, Takuma*; Kambe, Takashi*; Michiuchi, Takamasa*; Hayakawa, Hironori*; Oishi, Daisuke*; Hanasaki, Noriaki*; Ikeda, Naoshi*; Yoshii, Kenji

no journal, , 

LuFe$$_{2}$$O$$_{4}$$ is a ferroelectric material arising from the real-space ordering of Fe charges below 330 K. In this paper, we measured the magnetic-field dependence of dielectric response in this material. We report a change of dielectric constant depending on the measurement temperature and applied magnetic field.

Oral presentation

Dielectric properties on charge ordered ferroelectrics LuFe$$_{2}$$O$$_{4}$$

Ikeda, Naoshi*; Kambe, Takashi*; Komatsu, Takuma*; Michiuchi, Takamasa*; Hayakawa, Hironori*; Hanasaki, Noriaki*; Yoshii, Kenji; Matsuo, Yoji*; Mori, Shigeo*

no journal, , 

A review will be given on the new type of ferroelectric material LuFe$$_{2}$$O$$_{4}$$. This oxide becomes ferroelectric below about 330 K, owing to the charge-ordered arrangement of Fe ions on a triangular lattice: This is a novel mechanism of ferroelectricity. We discuss the experimental results obtained from resonant X-ray diffraction, dielectric response, polarization and magnetization to show some interesting properties of this new ferroelectric oxide.

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