研究者詳細 - 池田　直

論文 - 池田　直

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

S. Torigoe, Y. Ishimoto, Y. Aoishi, H. Murakawa, D. Matsumura, K. Yoshii, Y. Yoneda, Y. Nishihata, K. Kodama, K. Tomiyasu, K. Ikeda, H. Nakao, Y. Nogami, N. Ikeda, T. Otomo, N. Hanasaki

PHYSICAL REVIEW B 93 ( 8 ) 2016年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

We observed all-in type Nb tetrahedral displacement in nonmagnetic pyrochlore niobates A(2)Nb(2)O(7) (A = Nd0.5Ca0.5 and Y0.5Ca0.5) through the analysis of the neutron pair distribution function and the extended x-ray absorption function spectroscopy. The all-in type Nb tetrahedral displacement, which has the character of a charge singlet state, is driven by the formation of the bonding orbital. The diffuse scattering in the x-ray diffraction, which has the resonant component in the Nb L-3 edge, indicates that the all-in type Nb tetrahedral displacement has the periodicity with its short-range correlation.

DOI： 10.1103/PhysRevB.93.085109

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21aPS-115 金属-強誘電体接合系における触媒作用

重名智博, 狩野旬, 池田直, 藤井達生, 大久保智子

日本物理学会講演概要集 71 2708 - 2708 2016年

21aAF-3 BaTiO_3のバンド構造におけるイオン欠損効果

押目典宏, 狩野旬, 池田直, 寺西貴志, 大崎浩司, 藤井達生, 上田剛慈, 大久保智子

日本物理学会講演概要集 71 2691 - 2691 2016年

21aPS-116 Mnをドープした(YbFe_2O_4)_m(YbFeO_3)_n, m=1, n=1単結晶の磁性と誘電特性

烏谷友之, 藤原孝将, 藤井達生, 戸取和大, 古林宏之, 福永守, 堀部陽一, 狩野旬, 池田直

日本物理学会講演概要集 71.1 2709 2016年

Control of Fermi Level by Variation of Charge Ordering State in Yb1-xTixFe2O4

Tomoko Nagata, Hiroyuki Okazaki, Takanori Wakita, Tetsushi Fukura, Nobuyuki Iwata, Hiroshi Yamamoto, Takayoshi Yokoya, Naoshi Ikeda

Transactions of the Materials Research Society of Japan 41 ( 3 ) 269 - 271 2016年

記述言語：英語出版者・発行元：一般社団法人日本MRS

<p>Fermi level and valence state were investigated in RFe₂O₄ (R = Y, Dy, Ho, Er, Tm, Yb, Lu, Sc, or In), which shows magnetoelectric effect originating from charge and magnetic orders of Fe²⁺ and Fe³⁺. We succeeded in controlling the Fermi level of YbFe₂O₄ system by Ti⁴⁺ substitution for Yb³⁺. The variation in the ratio of Fe²⁺ to Fe³⁺ is suggested to the origin of the Fermi level variation. This report suggests the possibility of simple selection of conduction type in functional oxide.</p>

DOI： 10.14723/tmrsj.41.269

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Iron vacancy effect on the magnetization of YbFe2O4

K. Fujiwara, M. Miyajima, M. Fukunaga, J. Kano, H. Kobayashi, N. Ikeda

Transactions of the Materials Research Society of Japan 41 ( 1 ) 139 - 142 2016年

記述言語：英語出版者・発行元：一般社団法人日本MRS

We report the effect of iron vacancies on the magnetic property of spin and charge ordered system YbFe₂O₄ single crystals. The excess amount of iron compensates for the evaporation of iron during crystal growth. We concluded that samples grown with the standard method contain iron vacancies of more than 10%. It is considered that increasing the iron in the starting material recovers the iron stoichiometry, and the proper magnetic property appears. With recovery of the chemical stoichiometry, the magnetic hysteresis loop changes from a double loop to a single loop, which indicates the development of spin coherence and the appearance of a large ferrimagnetic domain. The anomaly found in the thermomagnetization curve at approximately 150 K, the so-called T_LT transition, disappears with better stoichiometry. This fact indicates that T_LT is not a kind of phase transition but an effect of iron vacancy. Our discovery demonstrates that most of the crystals used in RFe₂O₄ research might contain many iron vacancies. The confused discussions on this material about the spin order model, the charge order model, and so on might reconsider such chemical stoichiometry, including iron vacancies.

DOI： 10.14723/tmrsj.41.139

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Pressure dependence of far-infrared reflectance spectra in layered iron oxide LuFe2O4

T. Go, H. Okamura, G. Oohata, T. Nagata, T. Moriwaki, Y. Ikemoto, S. Mori, N. Ikeda, K. Mizoguchi

Transactions of the Materials Research Society of Japan 41 ( 1 ) 109 - 112 2016年

記述言語：英語出版者・発行元：一般社団法人日本MRS

The far-infrared reflectance spectra of layered iron oxide LuFe₂O₄ have been investigated at external pressure up to 8 GPa. The observed phonon modes continuously shift to the higher energy side with increasing pressure below 6 GPa. However, it is found that the spectral profile of the phonon modes drastically changes around 6 GPa. From the analysis of the phonon modes using a Lorentz oscillator model, it is shown that the spectral changes correspond to a structural phase transition that occurs at 6 GPa.

DOI： 10.14723/tmrsj.41.109

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Observation of Flux-Grown α-Fe2O3 Single Crystal at the Morin Transition by 57Fe Synchrotron Radiation Mössbauer Diffraction

Takaya Mitsui, Shin Nakamura, Naoshi Ikeda, Kosuke Fujiwara, Ryo Masuda, Yasuhiro Kobayashi, Makoto Seto

J. Phys. Soc. Jpn. 85 ( 5 ) 2016年

21pCC-5 核共鳴散乱回折装置による結晶サイト選択的メスバウアースペクトルの測定II

中村真一, 三井隆也, 藤原孝将, 池田直, 下村晋

日本物理学会講演概要集 71 1273 - 1273 2016年

層状鉄酸化物RFeMO4における短範囲秩序構造と誘電特性

吉本航, 藤原孝将, 池田直, 河口彰吾, 久保田佳基, 石井悠衣, 森茂生

日本物理学会講演概要集 71.2 2549 - 2549 2016年

記述言語：日本語出版者・発行元：一般社団法人日本物理学会

層状鉄酸化物RFe2O4は三角格子上で2価と3価のFeイオンが秩序化することにより特徴的な電荷秩序構造の形成を伴う強誘電体であり、また、低温で反強磁性転移を示すマルチフェロイック物質である。本研究では、Fe2+サイトをCo2+やCu2+等の遷移金属元素で置換することにより、特徴的な散漫散乱を与える局所構造が形成され、誘電特性等の物性に影響を与えることを見出した。また、RFe2O4型構造をもつ新しいIn系バナジウム酸化物についてもその構造と物性についても報告する予定である。

DOI： 10.11316/jpsgaiyo.71.2.0_2549

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マルチフェロイック{\it R}Fe$_{2}$O$_{4}$ ({\it R}: 希土類)の元素置換効果査読

吉井賢資, 船江岳史*, 水牧仁一朗*, 江尻宏紀*, 池田直*, 齋藤寛之, 松村大樹

Physica Status Solidi (C) 12 ( 6 ) 841 - 844 2015年6月

記述言語：英語

マルチフェロイック{\it R}Fe$_{2}$O$_{4}$ ($R$: Y, Ho-Lu, In)の元素置換効果について調べた。これまでほとんど報告例のない、非磁性のGa$^{3+}$を鉄サイトに置換した場合は、磁気転移温度$T_{\rm N}$が減少した。これは過去、{\it R}FeCoO$_{4}$などでも示した通り、鉄サイト間の磁気相互作用が弱まったためである。Ga$^{3+}$置換した場合、室温の誘電率は母物質とほぼ変わらない1000-10000程度であった。また、誘電損失が減少することも判明した。この理由については現在不明であるが、損失の減少はエネルギー利用効率の上昇を示しており、応用に有利である。また$R$サイトの置換も行い、Dy$^{3+}$のような大きな$R^{3+}$を10\%程置換できることが、放射光吸収分光により判明した。なお、置換試料では$T_{\rm N}$が5-10K上昇した。この現象の起源についても現状では不明であるが、室温でマルチフェロイック状態を実現する一つの方向性を示しており、興味深い結果である。

DOI： 10.1002/pssc.201400250

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Valence-specific magnetization of the charge-ordered multiferroelectric LuFe2 O4 using soft x-ray magnetic circular dichroism under 30 T pulsed high magnetic fields

Yasuo Narumi, Tetsuya Nakamura, Kota Saito, Takayuki Morioka, Yukimasa Fukada, Takashi Kambe, Naoshi Ikeda, Yoshinori Kotani, Toyohiko Kinoshita, Koichi Kindo, Hiroyuki Nojiri

Physical Review B - Condensed Matter and Materials Physics 91 ( 1 ) 2015年1月

掲載種別：研究論文（学術雑誌）

Soft x-ray magnetic circular dichroism (XMCD) have been measured on the single crystal of the charge-ordered type multiferroelectric material LuFe2O4. By comparing the XMCD results with the bulk magnetizations, the valence-specific magnetizations (VSMs) of Fe2+ and Fe3+ ions are obtained. Both Fe2+ and Fe3+ ions show positive and negative remanent VSMs below the spin ordering temperature TSO∼250 K, showing the ferrimagnetic long-range ordering directly. Both of the remanent VSMs disappear above the TSO and the field dependencies of the VSMs behave in paramagnetic fashions with convex and concave curvatures. However, the signs of the VSMs of Fe2+ and Fe3+ remain opposite, nevertheless the system is in a paramagnetic phase. This is direct evidence of the robust antiferromagnetic interaction between Fe2+ and Fe3+ ions even above the TSO. As temperature increases, furthermore, the opposite VSM of Fe3+ is reversed around the three-dimensional charge ordering temperature TCO∼330 K showing that both net magnetic moments of Fe2+ and Fe3+ become parallel to the applied magnetic field. Possible correlation between these unusual magnetic behaviors and the ferroelectric properties of LuFe2O4 is discussed.

DOI： 10.1103/PhysRevB.91.014410

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Valence-specific magnetization of the charge-ordered multiferroelectric LuFe2O4 using soft x-ray magnetic circular dichroism under 30 T pulsed high magnetic fields

Yasuo Narumi, Tetsuya Nakamura, Kota Saito, Takayuki Morioka, Yukimasa Fukada, Takashi Kambe, Naoshi Ikeda, Yoshinori Kotani, Toyohiko Kinoshita, Koichi Kindo, Hiroyuki Nojiri

PHYSICAL REVIEW B 91 ( 1 ) 2015年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

Soft x-ray magnetic circular dichroism (XMCD) have been measured on the single crystal of the charge-ordered type multiferroelectric material LuFe2O4. By comparing the XMCD results with the bulk magnetizations, the valence-specific magnetizations (VSMs) of Fe2+ and Fe3+ ions are obtained. Both Fe2+ and Fe3+ ions show positive and negative remanent VSMs below the spin ordering temperature T-SO similar to 250 K, showing the ferrimagnetic long-range ordering directly. Both of the remanent VSMs disappear above the TSO and the field dependencies of the VSMs behave in paramagnetic fashions with convex and concave curvatures. However, the signs of the VSMs of Fe2+ and Fe3+ remain opposite, nevertheless the system is in a paramagnetic phase. This is direct evidence of the robust antiferromagnetic interaction between Fe2+ and Fe3+ ions even above the T-SO. As temperature increases, furthermore, the opposite VSM of Fe3+ is reversed around the three-dimensional charge ordering temperature T-CO similar to 330 K showing that both net magnetic moments of Fe2+ and Fe3+ become parallel to the applied magnetic field. Possible correlation between these unusual magnetic behaviors and the ferroelectric properties of LuFe2O4 is discussed.

DOI： 10.1103/PhysRevB.91.014410

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10 fs Dynamics of Photoinduced Magnetic Transition in Double-Layered Charge Ordering in LuFe2O4 Under Interlayer Excitation 査読

Y. Sagae, K. Yamada, T. Ishikawa, K. Itoh, H. Itoh, T. Sasaki, T. Nagata, J. Kano, T. Kambe, S. Ishihara, N. Ikeda, S. Iwai

Springer Proceedings in Physics 162 (Ultrafast Phenomena XIX) 252 - 256 2015年1月

Mössbauer Spectroscopy of Novel Ferroelectric Materials

Shin Nakamura, Jun Kano, Norihiro Oshime, Naoshi Ikeda, Yasuhiro Kobayashi, Shinji Kitao, Makoto Seto

KURRI Progress Report 2014 78 2015年

Elemental substitution effects in multiferroic RFe2O4 (R: rare earths)

Kenji Yoshii, Takashi Funae, Masaichiro Mizumaki, Hiroki Ejiri, Naoshi Ikeda, Hiroyuki Saitoh, Daiju Matsumura

PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 12, NO 6 12 ( 6 ) 841 - 844 2015年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：WILEY-V C H VERLAG GMBH

We report the effects of elemental substitutions in multiferroic RFe2O4 (R: Y, Ho-Lu, In). The substitution by nonmagnetic Ga3+ at the Fe site, which has not been reported so far, shows a drastic decrease in the ferrimagnetic transition temperature (TN). This is plausibly owing to the suppression of magnetic interactions between Fe ions, based on our previous results of other substituted systems such as RFeCoO4. Dielectric constants near room temperature were comparable to those of RFe2O4. The suppression of dielectric loss in this system is suitable to application. The R-site substitution was also attempted by the large R3+ ions such as Dy3+. The solubility limit was up to similar to 10% of R ions. TN was raised by 5-10 K for Dy3+ substitution. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssc.201400250

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16aAD-4 複鉄酸化物YbFe_2O_4のFe 3p-3d共鳴光電子分光

福良哲司, 脇田高徳, 竹田彩, 寺嶋健成, 藤原孝将, 池田直, 村岡祐治, 横谷尚睦

日本物理学会講演概要集 70 2405 - 2405 2015年