※ 半角英数字
 年 ~ 
検索結果: 90 件中 1件目~20件目を表示


Initialising ...



Initialising ...


Initialising ...


Initialising ...


Initialising ...


Initialising ...


Initialising ...


Initialising ...



Hard X-ray photoelectron spectroscopy study of Pt/Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$

小畠 雅明; 吉井 賢資; 福田 竜生; 川崎 郁斗; 岡根 哲夫; 山上 浩志; 矢板 毅; 針井 一哉; 家田 淳一; 岡安 悟; et al.

JPS Conference Proceedings (Internet), 30, p.011192_1 - 011192_6, 2020/03

スピンゼーベック効果を示す系として注目されているPt/Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$(YIG)系に対し、放射光を用いた硬X線光電子分光(HAXPES)により表面及び界面の電子状態測定を行った。本系ではスピンゼーベック効果のほかに特異な性質を示すことが報告されている。例えば、外部磁場が存在しない状況でもホール効果を発現する。この起源として、YIG中のFe$$^{3+}$$イオンがPt膜に染み出し、磁性を持つ金属間化合物を生成している可能性が提案されている。そこでHAXPESの分析深さを利用し、界面近傍の鉄イオン等の電子状態を測定した。Ptの厚みが2nm, 5nm, 8nm, 10nmの試料を測定したところ、2nmと5nmの試料において鉄イオンの分析を行うことができた。Fe 1s光電子スペクトルからは、鉄イオンが3+のものと金属的な0価に近い2つの状態が存在することが判明し、上記の可能性を支持する結果が得られた。Pt 4fやO 1sスペクトルなども測定しており、詳しい結果は当日報告する。


Pyroelectric power generation from the waste heat of automotive exhaust gas

Kim, J.*; 山中 暁*; 村山 一郎*; 加藤 孝典*; 坂本 友和*; 川崎 卓郎; 福田 竜生; 関野 徹*; 中山 忠親*; 武田 雅敏*; et al.

Sustainable Energy & Fuels (Internet), 4(3), p.1143 - 1149, 2020/03

 被引用回数:0 パーセンタイル:100(Chemistry, Physical)

Waste heat is a potentially exploitable energy source but remains a problem awaiting a solution. To explore solutions for automobile applications, we investigate pyroelectric power generation from the temperature variation of exhaust gas using a novel electro-thermodynamic cycle. Niobium-doped lead zirconate titanate stannate (PNZST) ceramics were applied as pyroelectric materials, and their structural characteristics were investigated. In the driving cycle assessments (JC-08) using real exhaust gas, the maximum power generated was identified as 143.9 mW cm$$^{-3}$$ (777.3 J L$$^{-1}$$ per 1 cycle) over a temperature range of 150-220 $$^{circ}$$C and an electric field of 13 kV cm-1. The net mean generating power of the total driving cycle was 40.8 mW cm$$^{-3}$$, which is the most enhanced result in our power generating systems to date and 314 times greater than our first report. Materials with sharp transition behaviors with the temperature and electric field are worthy of study with regard to pyroelectric energy harvesting materials, and their corresponding crystal and domain structures were investigated to optimize performance.


Lattice dynamics in FeSe via inelastic X-ray scattering and first-principles calculations

村井 直樹; 福田 竜生; 中島 正道*; 河村 光晶*; 石川 大介*; 田島 節子*; Baron, A. Q. R.*

Physical Review B, 101(3), p.035126_1 - 035126_6, 2020/01

 被引用回数:0 パーセンタイル:100(Materials Science, Multidisciplinary)



Invariant incommensurate coherence length in spin-density-wave excitation of Cr$$_{0.99}$$Fe$$_{0.01}$$

平賀 晴弘*; 矢野 真一郎*; 福田 竜生

Journal of Magnetism and Magnetic Materials, 469, p.629 - 632, 2019/01

 被引用回数:0 パーセンタイル:100(Materials Science, Multidisciplinary)

Low-energy magnetic excitation of spin-density wave (SDW) in a single crystal of Cr$$_{0.99}$$Fe$$_{0.01}$$ was measured using cold neutron triple-axis spectroscopy. Because of the unchanged incommensurability and the constant line width in 2.5 $$leqslanthbaromegaleqslant$$ 6 meV, the magnetic excitation could not be explained with a conventional dispersion of $$hbaromega_qpropto q$$. In this paper, we conjectured the presence of standing waves, which would be excited in local spin matrices. The effectively vertical dispersion was attributed to the longitudinal spin fluctuation in the spin matrices. A series of low-energy magnetic excitations in Cr alloys could be understood with the coexistence of the standing waves and progressive waves such as spin waves.


Electrical and crystallographic study of an electrothermodynamic cycle for a waste heat recovery

Kim, J.*; 山中 暁*; 中島 啓*; 加藤 孝典*; Kim, Y.*; 福田 竜生; 吉井 賢資; 西畑 保雄; 馬場 将亮*; 武田 雅敏*; et al.

Advanced Sustainable Systems (Internet), 2(11), p.1800067_1 - 1800067_8, 2018/11

 被引用回数:1 パーセンタイル:80.97(Green & Sustainable Science & Technology)

An innovative electrothermodynamic cycle (pyroelectric effect with an external electric field) was recently presented, which is based on temporal temperature variations in wasted heat from engine exhaust gas. In this paper, for further improvement, a generating mechanism of the cycle is investigated using in-operando time-resolved synchrotron X-ray diffraction with generating assessment. The polarizations of the sample are gained from both crystal/domain changes and simultaneous electrical measurements. Three types of materials are prepared: soft and hard types of lead zirconate titanate (PZT) and lead magnesium niobate-lead titanate (PMN-PT). Among them, PMN-PT has the highest generating power. When an external electric field is applied, the PMN-PT exhibits only 180$$^circ$$ domain rotations, whereas PZTs exhibit both 90$$^circ$$ and 180$$^circ$$ rotations. A strong driving force for 180$$^circ$$ rotation depresses rotations in other angles and increases polarization changes. The results show that the material development, which has only 180$$^circ$$ switching domains, has potential for use in the establishment of a high-efficiency waste heat recovery system.


Temperature stability of PIN-PMN-PT ternary ceramics during pyroelectric power generation

茂呂 拓哉*; Kim, J.*; 山中 暁*; 村山 一郎*; 加藤 孝典*; 中山 忠親*; 武田 雅敏*; 山田 昇*; 西畑 保雄; 福田 竜生; et al.

Journal of Alloys and Compounds, 768, p.22 - 27, 2018/11

 被引用回数:5 パーセンタイル:36.4(Chemistry, Physical)

Relaxor-based ternary Pb(In$$_{1/2}$$Nb$$_{1/2}$$)O$$_3$$-Pb(Mg$$_{1/3}$$Nb$$_{2/3}$$)O$$_3$$-PbTiO$$_3$$ (PIN-PMN-PT) ceramics near a morphotropic phase boundary were grown, and their electrical properties at various temperatures were investigated in the electrothermodynamic cycle for the future environment-friendly automotive applications. Structural disordering, depending on the PIN content, influenced the diffuse phase transition between the tetragonal and cubic structures and contributed to the power-generating behavior. The net power-generating energies (P$$_{net}$$) were 2.43-3.01 mW/cm$$^3$$ at temperatures above 200$$^circ$$C and were maintained at above 1 mW/cm$$^3$$ over a temperature range of approximately 100 degrees. Therefore, the PIN-PMN-PT system has a possibility of a wider usage temperature range, the disordering of the perovskite crystal structure can be controlled, and it will be a candidate for the application of pyroelectric energy conversion system.


Effect of $$B$$-site randomness on the antiferroelectric/relaxor nature of the ground state; Diffuse and inelastic X-ray scattering study of Pb(In$$_{1/2}$$Nb$$_{1/2}$$)O$$_3$$

大和田 謙二*; 塚田 慎也*; 福田 竜生; 筒井 智嗣*; Baron, A. Q. R.*; 水木 純一郎*; 大和 英弘*; 安田 直彦*; 寺内 暉*

Physical Review B, 98(5), p.054106_1 - 054106_10, 2018/08

 被引用回数:0 パーセンタイル:100(Materials Science, Multidisciplinary)

The effect of $$B$$-site randomness on the antiferroelectric/relaxor nature of the ground state was investigated by studying diffuse and inelastic X-ray scattering from ordered and disordered Pb(In$$_{1/2}$$Nb$$_{1/2}$$)O$$_3$$ (O- and D-PIN) single crystals. The diffuse scattering measurement of O-PIN (antiferroelectric at $$T<T_N$$) shows the existence of ferroelectrically interactive local polarization above $$T_N$$. Inelastic X-ray scattering shows that the transverse-acoustic (TA) and transverse-optic (TO) modes are dominant at $$Tsim$$800 K, while the central peak (CP) and TA modes are coupled and majorly contribute to the critical behavior of the diffuse scattering at $$T_N$$. Upon these results, the $$B$$-site randomness is discussed in terms of suppressing the antiferroelectric instability and enhancing the polarization fluctuation.


Maximizing $$T_c$$ by tuning nematicity and magnetism in FeSe$$_{1-x}$$S$$_x$$ superconductors

松浦 康平*; 水上 雄太*; 新井 佑基*; 杉村 優一*; 前島 尚行*; 町田 晃彦*; 綿貫 徹*; 福田 竜生; 矢島 健*; 広井 善二*; et al.

Nature Communications (Internet), 8, p.1143_1 - 1143_6, 2017/10

 被引用回数:29 パーセンタイル:10.72(Multidisciplinary Sciences)

A fundamental issue concerning iron-based superconductivity is the roles of electronic nematicity and magnetism in realising high transition temperature ($$T_c$$). To address this issue, FeSe is a key material, as it exhibits a unique pressure phase diagram involving nonmagnetic nematic and pressure-induced antiferromagnetic ordered phases. However, as these two phases in FeSe have considerable overlap, how each order affects superconductivity remains perplexing. Here we construct the three-dimensional electronic phase diagram, temperature ($$T$$) against pressure ($$P$$) and iso-valent S-substitution ($$x$$), for FeSe$$_{1-x}$$S$$_x$$. By simultaneously tuning chemical and physical pressures, against which the chalcogen height shows a contrasting variation, we achieve a complete separation of nematic and antiferromagnetic phases. In between, an extended nonmagnetic tetragonal phase emerges, where $$T_c$$ shows a striking enhancement. The completed phase diagram uncovers that high-$$T_c$$ superconductivity lies near both ends of the dome-shaped antiferromagnetic phase, whereas $$T_c$$ remainslow near the nematic critical point.


Pyroelectric power generation with ferroelectrics (1-x)PMN-xPT

Kim, J.*; 山中 暁*; 中島 啓*; 加藤 孝典*; Kim, Y.*; 福田 竜生; 吉井 賢資; 西畑 保雄; 馬場 将亮*; 武田 雅敏*; et al.

Ferroelectrics, 512(1), p.92 - 99, 2017/08

 被引用回数:5 パーセンタイル:53.19(Materials Science, Multidisciplinary)

We have been investigating a novel electrothermodynamic cycle based on temporal temperature variations using the pyroelectric effect to utilize the waste heat as renewable energy. An improved generating performance with relaxer ferroelectric ceramics was achieved using 75Pb(Mg$$_{2/3}$$Nb$$_{1/3}$$)O$$_3$$-25PbTiO$$_3$$ which is well known for the high dielectric and pyroelectric properties. The potential was evaluated by using the hysteresis loops and generating properties are analyzed both in laboratory and engine dynamometer. Results showed 0.48 mW/cm$$^3$$ in engine dynamometer assessment, which is 3 times larger than the previous study using Pb(Zr,Ti)O$$_3$$.


Relationship between the material properties and pyroelectric-generating performance of PZTs

山中 暁*; Kim, J.*; 中島 啓*; 加藤 孝典*; Kim, Y.*; 福田 竜生; 吉井 賢資; 西畑 保雄; 馬場 将亮*; 山田 昇*; et al.

Advanced Sustainable Systems (Internet), 1(3-4), p.1600020_1 - 1600020_6, 2017/04



Mineralogical characterization of radioactive particles from Fukushima soil using $$mu$$-XRD with synchrotron radiation

甕 聡子*; 向井 広樹*; 綿貫 徹; 大和田 謙二; 福田 竜生; 町田 晃彦; 倉又 千咲*; 菊池 亮佑*; 矢板 毅; 小暮 敏博*

Journal of Mineralogical and Petrological Sciences, 111(5), p.305 - 312, 2016/10

 被引用回数:11 パーセンタイル:34.63(Mineralogy)



Effect of magnetism on lattice dynamics in SrFe$$_2$$As$$_2$$ using high-resolution inelastic X-ray scattering

村井 直樹*; 福田 竜生; 小林 達也*; 中島 正道*; 内山 裕士*; 石川 大介*; 筒井 智嗣*; 中村 博樹; 町田 昌彦; 宮坂 茂樹*; et al.

Physical Review B, 93(2), p.020301_1 - 020301_5, 2016/01

 被引用回数:6 パーセンタイル:54.42(Materials Science, Multidisciplinary)

Phonon spectra of detwinned SrFe$$_2$$As$$_2$$ crystals, as measured by inelastic X-ray scattering, show clear anisotropyaccompanying the magnetostructural transition at 200 K. We model the mode splitting using magnetic DFT calculations, including a phenomenological reduction in force-constant anisotropy that can be attributed to magnetic fluctuations. This serves as a starting point for a general model of phonons in this material applicable to both the antiferromagnetically ordered phase and the paramagnetic phase. Using this model, the measured splitting in the magnetic phase below T$$_N$$, and the measured phonon linewidth, we set a lower bound on the mean magnetic fluctuation frequency above T$$_N$$ at 210 K.


Science from the initial operation of HRC

伊藤 晋一*; 横尾 哲也*; 益田 隆嗣*; 吉澤 英樹*; 左右田 稔*; 池田 陽一*; 井深 壮史*; 川名 大地*; 佐藤 卓*; 南部 雄亮*; et al.

JPS Conference Proceedings (Internet), 8, p.034001_1 - 034001_6, 2015/09

Since the installation of the High Resolution Chopper Spectrometer, HRC, experiments using the HRC are being conducted to observe the dynamics in wide range of physics. Scientific results during the period since the initial construction are summarized.


Novel electrothermodynamic power generation

Kim, Y.*; Kim, J.*; 山中 暁*; 中島 啓*; 小川 孝*; 芹沢 毅*; 田中 裕久*; 馬場 将亮*; 福田 竜生; 吉井 賢資; et al.

Advanced Energy Materials, 5(13), p.1401942_1 - 1401942_6, 2015/07



Precise measurement of acoustic phonons in PrFeAsO$$_{1-y}$$

福田 竜生; Baron, A. Q. R.*; 内山 裕士*; 中村 博樹; 石角 元志*; 町田 昌彦; 社本 真一

SPring-8/SACLA利用研究成果集(Research Report) (インターネット), 3(2), p.290 - 293, 2015/07

Using inelastic X-ray scattering (IXS), we investigated acoustic phonons of PrFeAsO$$_{1-y}$$ precisely in order to select between two different models based on first principles calculations: the in-plane soft and clipped model. These models predict slightly different phonon intensities, and, in particular, different contamination of the longitudinal acoustic (LA) phonon spectra by transverse acoustic (TA) phonon modes. We were able to reduce the contamination with improved ${bfit Q}$ resolution, but the data quality was not sufficient to clearly decide between our models. Based on $$Q$$ dependence there appears to be slightly better agreement with the in-plane soft model at room temperature.


Direct observation of lattice symmetry breaking at the hidden-order transition in URu$$_2$$Si$$_2$$

利根川 翔*; 笠原 成*; 福田 竜生; 杉本 邦久*; 安田 伸広*; 鶴原 悠悟*; 渡邊 大樹*; 水上 雄太*; 芳賀 芳範; 松田 達磨*; et al.

Nature Communications (Internet), 5, p.4188_1 - 4188_7, 2014/06

 被引用回数:44 パーセンタイル:8.38(Multidisciplinary Sciences)

We report on the observation of lattice symmetry breaking from the fourfold to twofold structure by high-resolution synchrotron X-ray diffraction measurements at zero field. Small orthorhombic symmetry-breaking distortion sets in at the transition temperature with a jump, uncovering the weakly first-order nature of the hidden-order transition. This distortion is observed only in ultra pure samples, implying a highly unusual coupling nature between the electronic pneumaticity and underlying lattice.


Electronic structure of BaTiO$$_{3}$$ using resonant X-ray emission spectroscopy at the Ba-L$$_{3}$$ and Ti K absorption edges

吉井 賢資; 米田 安宏; Jarrige, I.*; 福田 竜生; 西畑 保雄; 鈴木 知史; 伊藤 嘉昭*; 寺嶋 孝仁*; 吉門 新三*; 福島 整*

Journal of Physics and Chemistry of Solids, 75(3), p.339 - 343, 2014/03

 被引用回数:5 パーセンタイル:74.11(Chemistry, Multidisciplinary)

強誘電体BaTiO$$_{3}$$3について、共鳴X線発光(RXES)及び部分蛍光法を用いたX線吸収分光(PFY-XAS)により電子状態を分析した。実験はSPring8の原子力機構ビームラインBL14B1と物質・材料研究機構ビームラインBL15XUで行った。Ba L$$_{3}$$吸収端でのPFY-XASスペクトルは、過去の文献とは異なり、キュリー点上下で変化しなかった。これは、Ba$$^{2+}$$イオンの位置はキュリー点で変位しないか変位が小さいことを示唆する。また、Ti K吸収端でのRXESスペクトルからは、発光ピークのエネルギーは入射光エネルギーによらずほぼ一定であった。この結果は、Ti 3d軌道が非局在的な性質を持っており、それによりTiイオンが変位して電気双極子の生成して強誘電体となるという、理論計算から提案された機構を支持することが分かった。


Evidence for a charge collective mode associated with superconductivity in copper oxides from neutron and X-ray scattering measurements of La$$_{2-x}$$Sr$$_x$$CuO$$_4$$

Park, S. R.*; 福田 竜生; Hamann, A.*; Lamago, D*; Pintschovius, L.*; 藤田 全基*; 山田 和芳*; Reznik, D.*

Physical Review B, 89(2), p.020506_1 - 020506_5, 2014/01

 被引用回数:17 パーセンタイル:31.82(Materials Science, Multidisciplinary)

In superconducting copper oxides, some Cu-O bond-stretching phonons around 70 meV show anomalous giant softening and broadening of electronic origin, and electronic dispersions have large renormalization kinks near the same energy. These observations suggest that phonon broadening originates from quasiparticle excitations across the Fermi surface and the electronic dispersion kinks originate from coupling to anomalous phonons. We measured the phonon anomaly in underdoped ($$x$$ = 0.05) and overdoped ($$x$$ = 0.20 and 0.25) La$$_{2-x}$$Sr$$_x$$CuO$$_4$$ by inelastic neutron and X-ray scattering with high resolution. Combining these and previously published data, we found that doping dependence of the magnitude of the giant phonon anomaly is very different from that of the ARPES kink, i.e., the two phenomena are not connected. We show that these results provide indirect evidence that the phonon anomaly originates from novel collective charge excitations as opposed to interactions with electron-hole pairs. Their amplitude follows the superconducting dome so these charge modes may be important for superconductivity.


Multi-spin-state dynamics during insulator-metal crossover in LaCoO$$_3$$

土居 篤典*; 藤岡 淳*; 福田 竜生; 筒井 智嗣*; 奥山 大輔*; 田口 康二郎*; 有馬 孝尚*; Baron, A. Q. R.*; 十倉 好紀*

Physical Review B, 90(8), p.081109_1 - 081109_4, 2014/01

 被引用回数:15 パーセンタイル:38.63(Materials Science, Multidisciplinary)

The phonon dynamics of spin-state crossover for perovskite LaCoO$$_3$$ was investigated using infrared and inelastic X-ray spectroscopy. We observed that the Co-O bond stretching phonons couples to the thermally excited spin-state. The momentum dispersion of the optical mode is anomalously dispersionless (less than 3 meV), and this supports the spin-state disproportionation scenario. The steep enhancement of spin-state fluctuation compared to the charge gap suggests the density dependent spin state disproportionation; a simple low spin (LS)/high spin (HS)- or LS/intermediate spin (IS)-state disproportionation is realized at the initial stage with dilute HS- (or IS-) state density, while the complex spin-state disproportionation involving all of the LS-, IS- and HS-state is formed when the density of HS- (or IS-) state is enhanced.


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

吉井 賢資; 池田 直*; 福山 諒太*; 永田 知子*; 神戸 高志*; 米田 安宏; 福田 竜生; 森 茂生*

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

 被引用回数:1 パーセンタイル:93.35(Physics, Condensed Matter)


90 件中 1件目~20件目を表示