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Journal Articles

Analysis of glass behavior of Lu$$_{2}$$Fe$$_{3}$$O$$_{7}$$ with distributed equivalent circuit model

Fukada, Yukimasa*; Fukuyama, Ryota*; Fujiwara, Kosuke*; Yoshii, Kenji; Shigematsu, Kei*; Azuma, Masaki*; Ikeda, Naoshi*

Journal of the Physical Society of Japan, 90(2), p.024710_1 - 024710_6, 2021/02

 Times Cited Count:2 Percentile:62.21(Physics, Multidisciplinary)

We report an analysis of the dielectric glasslike state of the spin- and charge-ordered system Lu$$_{2}$$Fe$$_{3}$$O$$_{7}$$, which has structural and physical properties analogous to those of the electronic ferroelectrics ${it R}$Fe$$_{2}$$O$$_{4}$$ (${it R}$: rare earth). Aging and memory effects of resistivity were found in the electric impedance response. We performed a numerical analysis with equivalent electric circuits that have a logarithmic Gaussian distribution of resistance and capacitance. The distribution parameters well explained the glassy nature of the electric and dielectric properties between 100 and 200 K and the distribution variations of charge- and magnetic-ordered domains underlying the glass nature.

Journal Articles

Insights into the proton transfer mechanism of a bilin reductase PcyA following neutron crystallography

Unno, Masayoshi*; Ishikawa, Kumiko*; Kusaka, Katsuhiro*; Tamada, Taro; Hagiwara, Yoshinori*; Sugishima, Masakazu*; Wada, Kei*; Yamada, Taro*; Tomoyori, Katsuaki; Hosoya, Takaaki*; et al.

Journal of the American Chemical Society, 137(16), p.5452 - 5460, 2015/04

 Times Cited Count:25 Percentile:65.65(Chemistry, Multidisciplinary)

Phycocyanobilin, a light-harvesting and photoreceptor pigment in higher plants, algae, and cyanobacteria, is synthesized from biliverdin IX$$alpha$$ (BV) by phycocyanobilin:ferredoxin oxidoreductase (PcyA) via two steps of two-proton-coupled two-electron reduction. We determined the neutron structure of PcyA from cyanobacteria complexed with BV, revealing the exact location of the hydrogen atoms involved in catalysis. Notably, approximately half of the BV bound to PcyA was BVH$$^{+}$$, a state in which all four pyrrole nitrogen atoms were protonated. The protonation states of BV complemented the protonation of adjacent Asp105. The "axial "water molecule that interacts with the neutral pyrrole nitrogen of the A-ring was identified. His88 N$$delta$$ was protonated to form a hydrogen bond with the lactam O atom of the BV A-ring. His88 and His74 were linked by hydrogen bonds via H$$_{3}$$O$$^{+}$$. These results imply that Asp105, His88, and the axial water molecule contribute to proton transfer during PcyA catalysis.

Journal Articles

Magnetic properties of R$$_{2}$$Fe$$_{3}$$O$$_{7}$$ (R=Yb and Lu)

Yoshii, Kenji; Ikeda, Naoshi*; Fukuyama, Ryota*; Nagata, Tomoko*; Kambe, Takashi*; Yoneda, Yasuhiro; Fukuda, Tatsuo; Mori, Shigeo*

Solid State Communications, 173, p.34 - 37, 2013/11

 Times Cited Count:3 Percentile:16.78(Physics, Condensed Matter)

We have investigated the magnetic properties of R$$_{2}$$Fe$$_{3}$$O$$_{7}$$ (R=Yb and Lu), which belongs to the homologous family of electronic ferroelectric RFe$$_{2}$$O$$_{4}$$. Magnetization measurements show ferrimagnetic ordering at the Neel temperature (T$$_{N}$$) of about 270 K, which is slightly higher than that of RFe$$_{2}$$O$$_{4}$$ (T$$_{N}$$ about 230-250 K). Observation of spin glass and exchange bias shows a coexistence of ferromagnetic and antiferromagneticinteractions, similarly to RFe$$_{2}$$O$$_{4}$$. This situation gives rise to a complex magnetic change and a broad peak of magnetic entropy change. Some characteristics, such as refrigeration temperatures higher than in RFe$$_{2}$$O$$_{4}$$, seem to offer a possibility of this system to applications.

Journal Articles

Exchange bias in multiferroic $$R$$Fe$$_{2}$$O$$_{4}$$ ($$R$$=Y, Er, Tm, Yb, Lu and In)

Yoshii, Kenji; Ikeda, Naoshi*; Nishihata, Yasuo; Maeda, Daisuke*; Fukuyama, Ryota*; Nagata, Tomoko*; Kano, Jun*; Kambe, Takashi*; Horibe, Yoichi*; Mori, Shigeo*

Journal of the Physical Society of Japan, 81(3), p.033704_1 - 033704_4, 2012/03

 Times Cited Count:10 Percentile:57.27(Physics, Multidisciplinary)

Exchange bias (EB) behavior has been observed for multiferroic $$R$$Fe$$_{2}$$O$$_{4}$$ ($$R$$=Y, Er, Tm, Yb, Lu and In). The materials with the small $$R$$$$^{3+}$$ ions ($$R$$=Tm, Yb, Lu and In) exhibit large EB fields ($$_sim^{>}$$ 1 kOe) below $$sim$$100-150 K. This property is rooted in a magnetically glassy state, arising from the competition between ferro- and antiferromagnetic domain interactions. In addition, the exchange bias field tends to be more enhanced for smaller $$R$$$$^{3+}$$ ions. Hence, the EB is controlled by the substitution at the $$R$$-site in this series.

Journal Articles

High pressure and temperature synthesis of Bi-based perovskite Bi$$_{0.5}$$Na$$_{0.5-x}$$Li$$_x$$)TiO$$_3$$

Fukunaga, Masanori; Yoneda, Yasuhiro; Fukuyama, Ryota*; Saito, Hiroyuki; Ikeda, Naoshi*; Katayama, Yoshinori

Transactions of the Materials Research Society of Japan, 35(1), p.111 - 114, 2010/03

High-pressure synthesis of bismuth based perovskite (Bi$$_{0.5}$$Na$$_{0.5-x}$$Li$$_x$$)TiO$$_3$$ (BNLT) ($$x$$=0.1, 0.15, 0.2, 0.25, 0.4, 0.5) was demonstrated. Single phase BNLTs with perovskite structure were successfully synthesized for $$x$$$$leq$$0.1 by the solid state reaction method. The solid phase reaction occurred in the pressure range of 6-10 GPa, and in the temperature range of 800-1200 $$^{circ}$$C. Two thermal anomalies were observed in single phase perovskite BNLT ($$x$$=0.1) as well as (Bi,Na)TiO$$_3$$. The cusp like anomaly at 210 $$^{circ}$$C was assigned to a rhombohedral-tetragonal structural phase transition. The finished products of $$x$$$$geq$$0.2 included three kinds of impurities, which were affected by the selection of starting materials.

Oral presentation

Magnetic properties and electronic properties of LuGaFeO$$_{4}$$

Kuroda, Tomoko*; Fukuyama, Ryota*; Kitamura, Satoshi*; Matsuo, Yoji*; Ikeda, Naoshi*; Kambe, Takashi*; Agui, Akane; Kimizuka, Noboru*

no journal, , 

no abstracts in English

Oral presentation

Successive charge-ordering transition in YFe$$_{2}$$O$$_{4}$$

Maeda, Daisuke*; Fukuyama, Ryota*; Kitamura, Satoshi*; Funae, Takeshi*; Matsuo, Yoji*; Ikeda, Naoshi*; Kambe, Takashi*; Kimizuka, Noboru*; Yoshii, Kenji

no journal, , 

We have investigated the successive phase transition in YFe$$_{2}$$O$$_{4}$$, which shows charge-ordering-induced ferroelectricity below about 330 K. This material has been reported to show complex phase transitions below 330 K. In this work we have studied the structure and physical properties of YFe$$_{2}$$O$$_{4}$$ synthesized in a variety of preparation conditions, and have found that slight changes of the conditions led to drastic alternations of physical properties. Details of the results will be shown at the conference.

Oral presentation

Magnetic and dielectric properties of Lu$$_{2}$$Fe$$_{3}$$O$$_{7}$$

Fukuyama, Ryota*; Yoshii, Kenji; Kuroda, Tomoko*; Kitamura, Satoshi*; Funae, Takeshi*; Matsuo, Yoji*; Ikeda, Naoshi*; Kimizuka, Noboru*; Kambe, Takashi*

no journal, , 

We have investigated the physical properties of Lu$$_{2}$$Fe$$_{3}$$O$$_{7}$$, which has a related structure to the electronic ferroelectric RFe$$_{2}$$O$$_{4}$$ (R: rare earths). Magnetic measurements showed that its magnetic transition temperature was about 260-270 K. Dielectric measurements showed that dielectric constants at room temperature were about 10000. This material also showed a magneto-dielectric effect at around room temperature, a result which is interesting from the viewpoints of both fundamental and applied science.

Oral presentation

Magnetic properties of single crystalline Lu$$_{2}$$Fe$$_{3}$$O$$_{7}$$

Yoshii, Kenji; Ikeda, Naoshi*; Fukuyama, Ryota*; Nagata, Tomoko*; Kambe, Takashi*; Yoneda, Yasuhiro; Fukuda, Tatsuo; Mori, Shigeo*

no journal, , 

The rare-earth iron oxides R$$_{2}$$Fe$$_{3}$$O$$_{7}$$ (R=Yb and Lu) are materials closely related to a multiferroic system RFe$$_{2}$$O$$_{4}$$, which shows a new type of ferroelectiricy (i.e., electronic ferroelectiricy) at 330 K owing to real-space charge ordering of Fe ions. In this work, we have investigated detailed magnetic properties of a single crystalline LuFe$$_{3}$$O$$_{7}$$. It was found that this oxide shows the magnetic transition temperature of 270 K, which is higher than that of the corresponding RFe$$_{2}$$O$$_{4}$$ (LuFe$$_{2}$$O$$_{4}$$), 240-250 K. AC magnetic susceptibility measurements exhibited spin-glass behavior at around the magnetic transition temperature. In addition, exchange bias and magnetocaloric effect were observed at low temperatures, similarly to RFe$$_{2}$$O$$_{4}$$. These phenomena are explained in connection with several factors, such as a coexistence of ferromagnetic and antiferromagnetic interactions between Fe ions.

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