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Journal Articles

Nanoscale ice-type structural fluctuation in spinel titanates

Torigoe, Shuhei*; Hattori, Takayuki*; Kodama, Katsuaki; Honda, Takashi*; Sagayama, Hajime*; Ikeda, Kazutaka*; Otomo, Toshiya*; Nitani, Hiroaki*; Abe, Hitoshi*; Murakawa, Hiroshi*; et al.

Physical Review B, 98(13), p.134443_1 - 134443_7, 2018/10

 Times Cited Count:2 Percentile:16.65(Materials Science, Multidisciplinary)

Journal Articles

Observation of all-in type tetrahedral displacements in nonmagnetic pyrochlore niobates

Torigoe, Shuhei*; Ishimoto, Yutaro*; Aoishi, Yuhei*; Murakawa, Hiroshi*; Matsumura, Daiju; Yoshii, Kenji; Yoneda, Yasuhiro; Nishihata, Yasuo; Kodama, Katsuaki; Tomiyasu, Keisuke*; et al.

Physical Review B, 93(8), p.085109_1 - 085109_5, 2016/02

 Times Cited Count:4 Percentile:26.78(Materials Science, Multidisciplinary)

Journal Articles

X-ray absorption spectra in pyrochlore niobates

Torigoe, Shuhei*; Ishimoto, Yutaro*; Hanasaki, Noriaki*; Nogami, Yoshio*; Matsumura, Daiju; Yoshii, Kenji; Yoneda, Yasuhiro; Nishihata, Yasuo

Journal of Physics; Conference Series, 320, p.012078_1 - 012078_4, 2011/09

 Times Cited Count:1 Percentile:37.04

The X-ray absorption spectra of some pyrochlore niobates reveal the valence of the Nb ion in each material, and the displacement of the Nb ions from the center of the oxygen octahedra in the pyrochlore niobates YCaNb$$_{2}$$O$$_{7}$$ and NdCaNb$$_{2}$$O$$_{7}$$, which is consistent with the previous report of the neutron diffraction.

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

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$$_{4}$$.

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.

Oral presentation

Charge-order structure and physical properties of YbFe$$_{2-x}$$Mn$$_{x}$$O$$_{4}$$

Matsumoto, Keisuke*; Matsuo, Yoji*; Oishi, Daisuke*; Akahama, Yuji*; Yoshii, Kenji; Hanasaki, Noriaki*; Kambe, Takashi*; Ikeda, Naoshi*; Kimizuka, Noboru*; Mori, Shigeo*

no journal, , 

We have investigated the charge-ordered structure and physical properties of YbFe$$_{2-x}$$Mn$$_{x}$$O$$_{4}$$. Electron diffraction measurements showed a disappearance of charge-ordered structure of Fe ions by the Mn substitution. The Mn substitution also led to a monotonic decrease in magnetic transition temperature, low-temperature magnetization and dielectric constants. The results are explained in connection with several factors such as short-range ionic order.

Oral presentation

X-ray absorption spectra and ferroelectricity in pyrochlore niobates

Nara, Shintaro*; Torigoe, Shuhei*; Hanasaki, Noriaki*; Nogami, Yoshio*; Matsumura, Daiju; Yoshii, Kenji; Yoneda, Yasuhiro; Nishihata, Yasuo

no journal, , 

We have investigated the physical properties of pyrochlore niobates YCaNb$$_{2}$$O$$_{7}$$ and NdCaNb$$_{2}$$O$$_{7}$$. From synchrotron X-ray absorption and thermogravimetric measurements, the average valence of Nb ion in these oxides was determined as 4.5+, indicating the existence of charge frustration on the Nb site. These oxides have been found to show some intriguing properties such as the absence of magnetic moment of Nb, large thermoelectric effect and ferroelectricity. Possible origins of these phenomena are discussed on the basis of results of X-ray absorption measurements.

Oral presentation

Magnetic/dielectric properties and charge ordering phenomenain YbFe$$_{2-x}$$Mn$$_{x}$$O$$_{4}$$, 2

Matsumoto, Keisuke*; Hoshiyama, Takuya*; Oishi, Daisuke*; Akahama, Hiroshi*; Yoshii, Kenji; Kano, Jun*; Hanasaki, Noriaki*; Kambe, Takashi*; Ikeda, Naoshi*; Mori, Shigeo*

no journal, , 

We have investigated the physical properties of YbFe$$_{2-x}$$Mn$$_{x}$$O$$_{4}$$, a derivative system of the electronic ferroelectric RFe$$_{2}$$O$$_{4}$$ (R: rare earths). Electron diffraction measurements showed taht long-range charge ordering of the Fe-3d charges was observed at room temperature for x=0; this ordering is the origin of ferroelectricity. The x=0.1 oxide showed diffuse scattering patterns at room temperature, instead of the charge-ordered pattern. Thus, 5% Mn substitution can collapse the long-range charge ordering. We will also present the correlation between the magnetic/dielectric properties and the crystal structure.

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