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Journal Articles

Multiferroic character and magnetic phase of LuFe$$_{2}$$O$$_{4}$$

Oishi, Daisuke*; Hayakawa, Hironori*; Akahama, Hiroshi*; Ikeda, Naoshi*; Kambe, Takashi*; Matsuo, Yoji*; Kimizuka, Noboru*; Kano, Jun*; Yoshii, Kenji

Ferroelectrics, 415(1), p.51 - 56, 2011/10

 Times Cited Count:5 Percentile:27.56(Materials Science, Multidisciplinary)

The variation of AC dielectric constant in the function of the DC magnetic fields was found in low oxygen vacant LuFe$$_{2}$$O$$_{4}$$ single crystal in which the electric polarization arise from the polar charge ordering. These magneto-electric coupling should be explained by a novel mechanism where the boundary motion of the polar charge ordered domain is affected by the magnetic (spin) domain boundary motion.

Journal Articles

Growth and characterization of bismuth magnesium titanate Bi(Mg$$_{1/2}$$Ti$$_{1/2}$$)0$$_3$$

Yoneda, Yasuhiro; Saito, Hiroyuki; Yoshii, Kenji; Nishida, Takashi*; Hayakawa, Hironori*; Ikeda, Naoshi*

Key Engineering Materials, 421-422, p.30 - 33, 2010/00

Polycrystalline Bi(Mg$$_{1/2}$$Ti$$_{1/2}$$)O$$_3$$ samples were prepared under high pressure. A mixed powder of Bi$$_2$$O$$_3$$, Ti$$_2$$O$$_3$$ and MgO with a prescribed ratio was packed into platinum cell and was heated a cubic anvil-type apparatus at 6.5 GPa and 1000 $$^circ$$C. The obtained samples were characterized by powder X-ray diffraction measurements. Although some impurity peaks existed, the main peaks were perovskite peaks. The structure of Bi(Mg$$_{1/2}$$Ti$$_{1/2}$$)O$$_3$$ is rhombohedral, as well as BiFeO$$_3$$. The D-E hysteresis loop was not saturated due to the impurities, but the possibility as ferroelectric can be expected enough.

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

Local structure analysis of cubic perovskite CaCu$$_3$$Ti$$_4$$O$$_{12}$$

Yoneda, Yasuhiro; Yoshii, Kenji; Hayakawa, Hironori*; Ikeda, Naoshi*

Transactions of the Materials Research Society of Japan, 34(1), p.15 - 18, 2009/03

Recently, there has been considerable interest in the dielectric properties of the cubic perovskite CaCu$$_3$$Ti$$_4$$O$$_{12}$$. The material has shown to have high and relatively temperature independent dielectric permittivity over a wide temperature range from 100 to 600 K. Below $$sim$$100 K the permittivity drops by almost three orders of magnitude, but is not accompanied by a structural phase transition. We studied CaCu$$_3$$Ti$$_4$$O$$_{12}$$ hoping to find signatures of local structural distortions that may explain the observe anomalies in the dielectric properties. Experiments were carried out using synchrotron radiation at several temperatures between room temperature and 10 K. Reconsideration is necessary for interpreting a huge permittivity by the local disorder model.

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

Local structural change of CaCu$$_3$$Ti$$_4$$O$$_{12}$$ in low temperature phase

Yoneda, Yasuhiro; Yoshii, Kenji; Hayakawa, Hironori*; Aoyagi, Rintaro*; Ikeda, Naoshi*

no journal, , 

Insulating cubic compound CaCu$$_3$$Ti$$_4$$O$$_{12}$$ (CCTO) has attracted much interest because of its giant change in the dielectric response with temperature. This compound possesses a low-frequency dielectric constant, $$epsilon$$ $$sim$$ 10$$^4$$, which is only varying in the temperature range 100 - 600K. However, dielectric measurements indicated that the CCTO is electrically inhomogenious by analyzing its impedance. The inhomogenity may originated by grain and grain-boundary contributions. We performed synchrotron X-ray pair-distribution function (PDF) analysis in order to visualize this inhomogenity. The obtained PDF changed depending on the grain size. The PDF showed that the origin of huge dielectric constant is extrinsic Maxwell-Wagner type due to the sample inhomogenity.

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

Production of radioisotope from lithium using laser induced proton beams

Ogura, Koichi; Shizuma, Toshiyuki; Hayakawa, Takehito; Orimo, Satoshi; Sagisaka, Akito; Nishiuchi, Mamiko; Mori, Michiaki; Yogo, Akifumi; Pirozhkov, A. S.; Sugiyama, Hironori*; et al.

no journal, , 

Protons with energies up to 3 MeV have been generated by the irradiation of a 7.5 $$mu$$m thickness target by a 1 Hz table top laser with intensity of 700mJ. These protons were used to induce the nuclear reaction 7Li(p,n)7Be. Simultaneously, energy of proton was detected by a time of flight method.

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

Local structure of triangular-lattice oxides LuFeMO$$_{4}$$(M=Co,Cu)

Matsuo, Yoji*; Mori, Shigeo*; Yoshii, Kenji; Hayakawa, Hironori*; Ikeda, Naoshi*

no journal, , 

We have investigated the local structure of LuFe(Co,Cu)O$$_{4}$$, in which half of Fe ions are replaced by Co and Cu in electronic ferroelectric LuFe$$_{2}$$O$$_{4}$$. It was found that the electron diffraction patterns at room temperature showed diffuse scattering besides fundamental spots. Based on calculations for possible model structures, we suggest the existence of 4-point clusters consisting of Fe and Co/Cu, which is likely the origin of dielectric constant of 10-1000 at room temperature.

Oral presentation

Charge ordering state in the electronic ferroelectric LuFe$$_{2}$$O$$_{4}$$ studied by use of synchrotron radiation

Kubota, Masato*; Hayakawa, Hironori*; Oishi, Daisuke*; Akahama, Yuji*; Yoshii, Kenji; Kambe, Takashi*; Ikeda, Naoshi*

no journal, , 

Charge-ordered state of electronic ferroelectric LuFe$$_{2}$$O$$_{4}$$ was studied by use of synchrotron radiation. We have performed X-ray diffraction measurements at Fe K- and L-edges for a single-crystal LuFe$$_{2}$$$$_{4}$$ with applying currents at around room temperature. It was observed that the charge-ordered state changed depending on parameters such as the current density and the direction of current. We will discuss detailed results of experiments and at the conference.

Oral presentation

Applied-electric-field dependence of charge ordered phase in the trianglular-lattice system LuFe$$_{2}$$O$$_{4}$$

Hayakawa, Hironori*; Kubota, Masato*; Oishi, Daisuke*; Akahama, Yuji*; Matsuo, Yoji*; Ikeda, Naoshi*; Kambe, Takashi*; Kimizuka, Noboru*; Yoshii, Kenji

no journal, , 

We have investigated the change of charge-ordered state in LuFe$$_{2}$$O$$_{4}$$ caused by an applied electric field. The application of the field above a threshold led to a drastic decrease in resistivity; this behavior corresponds to the change of charge-ordered structure observed using synchrotron radiation. More details will be shown at the conference.

Oral presentation

Multiferroic behavior and magnetic phase diagram of LuFe$$_{2}$$O$$_{4}$$

Oishi, Daisuke*; Hayakawa, Hironori*; Akahama, Yuji*; Funae, Takeshi*; Matsuo, Yoji*; Ikeda, Naoshi*; Kambe, Takashi*; Kimizuka, Noboru*; Yoshii, Kenji

no journal, , 

We have investigated the multiferroic behavior and the magnetic phase diagram of single-crystalline electronic ferroelectric LuFe$$_{2}$$O$$_{4}$$. Dielectric measurements under an applied magnetic field showed large magneto-capacitance at around room temperature. A complex magnetic phase diagram was obtained from detailed magnetic measurements below about room temperature. More details will be shown at the conference.

Oral presentation

Activity produced by laser induced proton beams

Ogura, Koichi; Shizuma, Toshiyuki; Hayakawa, Takehito; Orimo, Satoshi; Sagisaka, Akito; Nishiuchi, Mamiko; Mori, Michiaki; Yogo, Akifumi; Pirozhkov, A. S.; Sugiyama, Hironori*; et al.

no journal, , 

Ultrashort and high intensity laser can induce high energy protons. Proton beams have a wide range of applications such as in the production of radioisotopes and proton therapy. An energy of the proton beam has a wide distribution. The distribution of activity in depth is calculated while laser induced protons are injected into an iron plate.

Oral presentation

3D CFD calculation for confirming an effect of structure to suppress gas entrainment from liquid surface of Sodium-cooled Fast Reactor

Nakamura, Hironori*; Uchita, Masato*; Hayakawa, Satoshi*; Matoba, Ichiyo*; Watanabe, Osamu*; Onoda, Yuichi; Tanaka, Masaaki

no journal, , 

no abstracts in English

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