Details of a Researcher - Matoba, Masanori

Papers - Matoba, Masanori

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複合アニオン層状化合物 LaCu_1-δS_0.5Se_0.5O (δ ~ 0.01) 多結晶縮退半導体の光学バンドギャップ内構造

東伸彦, 澤田拓希, 伊藤大平, 坂上良介, 的場正憲, 臼井秀知, 神原陽一

材料の科学と工学 58 ( 2 ) 22 - 26 2021.04

Research paper (scientific journal), Joint Work, Accepted

Thermoelectric transport properties of the van der Waals-type layered rhombohedral SnAs-based compound, EuSn₂As₂

Ryosuke Sakagami, Yosuke Goto, Harunari Karimata, Nobuhiko Azuma, Michitaro Yamaguchi, Suguru Iwasaki, Manami Nakanishi, Itsuki Kitawaki, Yoshikazu Mizuguchi, Masanori Matoba, Yoichi Kamihara

Japanese Journal of Applied Physics 60 ( 3 ) 2021.03

Research paper (scientific journal), Joint Work, Accepted, ISSN 00214922

The thermoelectric transport properties of the van der Waals-type layered rhombohedral SnAs-based compound, EuSn2As2, have been investigated. A densified polycrystalline sample of EuSn2As2 with porosity (φ) of 2.4(9) vol.% exhibited a weak orientation to the c-axis for hexagonal coordination system; the weak orientation is parallel (P ∥) to the pressing direction of hot pressing. Measurements of electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ) were conducted perpendicular (P ⊥) to the pressing direction. The experimental values of ρ and S exhibit metallic temperature dependence and p-type carrier polarity. The power factor (P) was 0.51(8) mW m-1 K-2 at 673(4) K. Using the Wiedemann-Franz-Lorenz law, the phonon thermal conductivity (κ ph) was estimated to be 0.4(6) W m-1 K-1 at 673(6) K. The dimensionless figure of merit, ZT, was 0.092(17) at 673(3) K.

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Proposal of disruptive computing (A computing-domain-oriented approach)

T. Baba, Y. Shimada, S. Kawamura, M. Matoba, T. Fukushima, S. Fujii, T. Nagano, Y. Katsumata, N. Kochi, Y. Kimura

Japanese Journal of Applied Physics 59 ( 5 ) 050503-1 - 050503-13 2020.05

Research paper (scientific journal), Joint Work, Accepted, ISSN 00214922

The advanced data processing on the edge devices is getting much attention in addition to the performance of cloud computing for big data analysis and artificial intelligence for the advanced cyber-physical systems and Internet of Things. This paper shows the challenges of research and development on disruptive computing which enhance the conventional computing system with high performance and low power consumption. Future R&D challenges in computing technologies involve all technology layers including algorithms, packaging, software, architecture, circuits, devices, and materials. It is important from the perspective of social implementation and efficiency to select technologies suitable for important applications from each technology layer specific to the computing domain and with consideration for the timeline, and to develop technologies through a vertical integration approach. The promoting method of implementing such R&D is also described.

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混合アニオン層状化物Sr₂CrFeAsO_3-δの電子磁気相図

山口道太郎, 藤岡弘孝, 大塚貴史, 瀬戸誠, 北尾真司, 的場正憲，神原陽一

日本磁気学会論文特集号 (日本磁気学会) 3 28 - 33 2019.05

Research paper (scientific journal), Joint Work, Accepted

Superconducting properties of a mixed anion layered compound, Ca and F co-doped LaFeAsO with T_c = 31.5 K

Kodai Kaneyasu, Ryosuke Sakagami, Masanori Matoba, Yoichi Kamihara

Japanese Journal of Applied Physics (Japanese Journal of Applied Physics) 58 ( 3 ) 030911.1 - 030911.5 2019.03

Research paper (scientific journal), Joint Work, Accepted, ISSN 00214922

Polycrystalline Ca and F co-doped LaFeAsO samples (La1-xCaxFeAsO1-yFy) were synthesized by solid-state reactions. Samples with nominal composition: (y - x) ≤ 0.05 did not show superconductivity at temperatures T > 4.2 K, although an anomalous kink of the ρ-T curves, which is related to crystallographic phase transitions, was observed at T ∼ 150 K. Samples with nominal composition: (y - x) ≥ 0.15 did exhibit superconductivity. The superconducting transition temperature (T c) of co-doped LaFeAsO with nominal composition: (x, y) = (0.25, 0.50) was determined to be T c = 31.5 K, which is higher than the highest T c value observed for LaFeAsO1-xFx materials synthesized under ambient pressure.

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Superconducting transition temperatures in the electronic and magnetic phase diagrams of Sr₂VFeAsO_3-δ, a superconductor

Yujiro Tojo, Taizo Shibuya, Tetsuro Nakamura, Koichiro Shoji, Hirotaka Fujioka, Masanori Matoba, Shintaro Yasui, Mitsuru Itoh, Soshi Iimura, Hidenori Hiramatsu, Hideo Hosono, Shigeto Hirai, Wendy Mao, Shinji Kitao, Makoto Seto, and Yoichi Kamihara

Journal of Physics: Condensed Matter 31 115801 (14 pages) 2019.01

Research paper (scientific journal), Joint Work, Accepted

We elucidate the magnetic phases and superconducting (SC) transition temperatures (Tc) in Sr2VFeAsO3−δ(21113V), an iron-based superconductor with a thick-blocking layer fabricated
from a perovskite-related transition metal oxide. At low temperatures (T<37.1 K), 21113V exhibited a SC phase in the range 0.031⩽δ⩽0.145 and an antiferromagnetic (AFM) iron
sublattice in the range 0.267⩽δ⩽0.664. Mixed-valent vanadium exhibited a dominant AFM phase in 0.031⩽δ⩽0.088, and a partial ferrimagnetic (Ferri.) phase in the range 0.124⩽δ⩽0.664. The Ferri. phase was the most dominant at a δ value of 0.267, showing an AFM phase of Fe at T<20 K. Increasing the spontaneous magnetic moments reduced the magnetic shielding volume fraction due to the SC phase. This result was attributed to the magnetic phase of vanadium, which dominates the superconductivity of Fe in 21113V. The
Tc–δ curve showed two maxima. The smaller and larger of Tc maxima occurred at δ=0.073 and δ=0.145, respectively; the latter resides on the phase boundary between AFM and the
partial Ferri. phases of vanadium. 21113V is a useful platform for verifing new mechanisms of Tc enhancement in iron-based superconductors.

混合アニオン層状化合物LaCuSeOの光学バンドギャップ内構造

東伸彦，加藤達輝，中西愛，的場正憲，木方邦宏，李哲虎，神原陽一

材料の科学と工学 (日本材料科学会) 55 ( 5 ) 168 - 172 2018.11

Joint Work, Accepted

アンモニア合成新触媒Ru担持[Ca₂₄Al₂₈O₆₄]^4-(e^-)₄の表面再構成予測

中西愛, 木下拓郎, 的場正憲, 神原陽一

材料の科学と工学 (日本材料科学会) 55 ( 5 ) 173 - 179 2018.11

Research paper (scientific journal), Joint Work, Accepted

2012年にKitanoらにより室温で安定な電子化物(エレクトライド)[Ca24Al28O64]4+(e-)4 (Ru/C12A7:e-)を担体とし, Ru金属微粒子を担持した構造が, アンモニア合成の高効率触媒として働くことが報告された. われわれは, その機構を密度汎関数理論を用いて, 部分的ながら解析した. スラブモデルを用いて, C12A7:e-上に存在するRu原子層の安定性を検討したところ, Ru原子層一層の場合にのみ, C12A7とRuの双方が固体表面に安定に露出することが明らかになった.

NMR study of the layered cobalt oxyphosphide Sr₂Sc(Co_1-xFe_x)PO₃

Ko-ichi Magishi, Ryo Watanabe, Akihiko Hisada, Takahito Saito, Kuniyuki Koyama, Satoshi Okada, Yoichi Kamihara, Naoki Ohkubo, Shuichi Ban, and Masanori Matoba

Journal of Physics: Conference Series 969 012068 (5 pages) 2018.04

Research paper (scientific journal), Joint Work, Last author, Accepted

We report the results of 31P-nuclear magnetic resonance (NMR) measurements on the layered cobalt oxyphosphide Sr2Sc(Co1-xFe x )PO3 in order to investigate the magnetic properties at low temperatures from a microscopic view point. The 31P-Knight shifts measured at the resonance peak maximum of Sr2Sc(Co1-xFe x )PO3 have positive values and are T-independent in an entire temperature range, and the absolute value decreases with increasing Fe content. Also, the nuclear spin-lattice relaxation rate 1/T 1 is almost proportional to the temperature at low temperatures. The magnitude of 1/T 1 T decreases with increasing the Fe content, which suggests the decrease of the density of states around the Fermi level.

Transport Properties of the Layered Transition Metal Oxypnictide Sr₂ScCo_1-xFe_xPO₃ with Fe-doped Co_1-xFe_xP

Satoshi Okada, Yoichi Kamihara, Naoki Ohkubo, Shuichi Ban, and Masanori Matoba

Journal of Physics: Conference Series 969 012032 (6 pages) 2018.04

Research paper (scientific journal), Joint Work, Last author, Accepted

Polycrystalline samples of novel oxypnictides, Sr 2 ScCo 1-x Fe x PO 3 , with Fe-doped Co 1-x Fe x P layer were synthesized, and their resistivities and Seebeck coefficients were measured. These materials, Sr 2 ScCo 1-x Fe x PO 3 , crystallize in a layered structure which represent an alternative stack of ThCr 2 Si 2 type Co 1-x Fe x layers and K 2 NiF 4 type Sr 2 ScO 3 layers. The resistivities (ρ) decrease with decreasing temperature like a metal. The Seebeck coefficients (S) show negative values at room temperature, while the S show positive values for x = 0.04-0.7 at low temperature.

Superconducting critical current densities for Sr₂VFeAsO_3-δ wires fabricated by ex-situ powder-in-tube process

Suguru Iwasaki, Masanori Matoba, and Yoichi Kamihara

Materials Science Society of Japan (Materials Science Society of Japan) 55 ( 2 ) 77 - 81 2018.04

Research paper (scientific journal), Joint Work, Accepted

SnAs層を含む六方晶層状化合物EuSn₂As₂の多結晶合成

坂上良介, 後藤陽介, 水口佳一, 的場正憲, 神原陽一

材料の科学と工学 (日本材料科学会) 55 ( 2 ) 140 - 144 2018.04

Research paper (scientific journal), Joint Work, Accepted

新規熱電変換材料として期待されるSnAs層をもつEuSn2As2の多結晶合成の詳細を報告する。固相反応に用いるルツボとして、アルミナとカーボンの二種を検討し、いずれの場合も主相としてEuSn2As2相を得た。カーボンを使用した場合に、自己フラックとしての、Sn以外の異相の検出されない試料を得た。本報告は、2017年のArguillaらによる試料合成につづいて、2例目であり、Arguillaらの試料と格子定数が異なる。

鉄系超伝導体LaFeAsO_1-xF_x中の磁気モーメント消失に関する計算化学的検証

金安航大, 日比野拓, 的場正憲, 神原陽一

材料の科学と工学 (日本材料科学会) 54 ( 4 ) 140 - 144 2017.08

Research paper (scientific journal), Joint Work, Accepted

The electronic structure of structurally strained Mn₃O₄ postspinel and the relationship with Mn₃O₄ spinel

Shigeto Hirai, Yosuke Goto, Yuki Sakai, Atsushi Wakatsuki, Yoichi Kamihara, and Masanori Matoba

Journal of the Physical Society of Japan 84 ( 11 ) 114702 (6 Pages) 2015.10

Research paper (scientific journal), Joint Work, Last author, Accepted

Mn3O4は15 GPa 以上の高圧下で、スピネル構造からポストスピネル構造に転移し、低温から室温にかけて、逐次結晶構造相転移が生じることがHiraiらにより確かめられている。本論文は、粉末の反射率分光法、及び密度汎関数理論を用いてポストスピネル型Mn3O4の電子磁気構造を、実験的、理論的に明らにする。Mn3O4は絶縁体であり、伝導体に存在するエネルギーの異なる２つの状態密度の存在は、実験的にも示された。

Electrical and Thermal Transport of Layered Bismuth-chalcogenide EuBiS₂F at temperatures between 300 and 623 K

Yosuke Goto, Joe Kajitani, Yoshikazu Mizuguchi, Yoichi Kamihara, and Masanori Matoba

Journal of the Physical Society of Japan 84 ( 8 ) 085003 (2 pages) 2015.07

Research paper (scientific journal), Joint Work, Accepted

層状ビスマス硫化物 EuBiS2Fの電気的熱的輸送現象を報告する。この物質において、Eu 4f-Bi6p軌道混成とそれに起因する興味深い輸送現象が予想されている。しかしながら300 K以上の温度領域では、EuBiS2Fで観察される輸送現象は4f軌道が電気的性質に寄与しないLaBiS2Oと同様であり、Eu 4f-Bi 6p軌道混成の影響は定かで無い。EuBiS2Fの格子熱伝導率はSrBiS2Fに比べて小さい。これはEuがSrに比べ、質量数が大きいことに起因する。

Electrical / thermal transport and electronic structure of binary cobalt pnictides CoPn₂ (Pn = As and Sb)

Yosuke Goto, Syuhei Miyao, Yoichi Kamihara, and Masanori Matoba

AIP Advances 5 ( 6 ) 067147 (7pages) 2015.06

Research paper (scientific journal), Joint Work, Last author, Accepted

ナノスケール熱制御によるデバイス革新－フォノンエンジニアリング－

馬場寿夫, 斎藤広明, 永野智己, 松下伸広, 的場正憲, 佐藤勝昭, 曽根純一

クリスタルレターズ ( 59 ) 64 - 67 2015.05

Research paper (scientific journal), Joint Work, Accepted

A Ferromagnetic Quantum Critical Pont in Heavy-Fermion Iron Oxypnictide CeFe_1-xCr_xPO

Tomohiro Okano, Shinji Kitao, Makoto Seto, Toshiyuki Atou, Mitsuru Itoh, Masanori Matoba, Yoichi Kamihara

Journal of Applied Physics 117 17E123 (4 pages) 2015.04

Research paper (international conference proceedings), Joint Work, Accepted

量子相転移(QCP)は、磁性に近接し、しばしば超伝導相の出現を伴うことから、多くの研究者に着目される物理現象である。本報告では、重い電子系で生じる強磁性的なQCPに関して予備的な報告を行う。Ce(Fe1-xCrx)PO (x = 0.10, 0.20, 0.30)多結晶試料は、固相反応により作製された。各試料の結晶相はX線回折により確認した。各試料の磁気転移温度はアロットプロットにより求めた。Ce(Fe1-xCrx)POのQCPは、x=0.00-0.10に存在する。

Magnetic properties of Shandite-phase Co_3-xFe_xSn₂S₂ (x = 0-1.0) obtained with high pressure synthesis

Yuki Sakai, Ryota Tanakadate, Masanori Matoba, Ikuya Yamada, Norimasa Nishiyama, Tetsuo Irifune, Kenichi Funakoshi, Takehiro Kunimoto, Yuji Higo, and Yoichi Kamihara

Journal of the Physical Society of Japan 84 ( 4 ) 044705 (6 pages) 2015.03

Research paper (scientific journal), Joint Work, Accepted

シャンド鉱型強磁性体Co3-xFexSn2S2の室温から1673 K、常圧から11 GPaの高温高圧において、その場エネルギー分散X線回折パターンを測定し、Feの固溶限界の圧力依存性を明らかにした。常圧下ではFeの固溶はx=0.6が上限であるのに対し、高圧下ではx=1.0程度まで固溶限界が上昇する。それに伴い、強磁性転移温度は、母相の175 Kよりx=1.0の68 Kまで減少する。これらの結果は擬ポテンシャルによる密度汎関数法による電子状態計算結果と矛盾しない。

Effect of Sn-substitution on Thermoelectric Properties of Copper-based Sulfide, Famatinite Cu₃SbS₄

Yosuke Goto, Yuki Sakai, Yoichi Kamihara, and Masanori Matoba

Journal of the Physical Society of Japan 84 ( 4 ) 044706 (5 pages) 2015.03

Research paper (scientific journal), Joint Work, Accepted

Electronic Structure and Transport Properties of Cu-deficient Kuramite Cu_3-xSnS₄

Yosuke Goto, Yuki Sakai, Yoichi Kamihara, and Masanori Matoba

Japanese Journal of Applied Physics 54 ( 2 ) 021801 (5 pages) 2015.01

Research paper (scientific journal), Joint Work, Last author, Accepted

銅欠陥のあるクラマイト型Cu3-xSnS4 (CTS)の電気/熱輸送特性を明らかにした。CTSの結晶学的な特徴はCuとSnのサイト間の構成イオンの部分的な交換(アンチサイト)である。CTSはバンド絶縁体的な挙動を示すCu2ZnS4とCu3SbS4と異なり, キャリアドープにより 10の21乗程度のキャリア密度を示す金属であり, 格子熱伝導率は 2 Wm-1K-1であった.この輸送現象はCu 3d と S 3p 軌道に由来する.

Transport Properties of the layered transition Metal Oxypnictide Sr₂ScMPO₃ with MP layers (M = Mn, Ni and Co_0.5Fe_0.5)

Satoshi Okada, Yoichi Kamihara, Naoki Ohkubo, Shuichi Ban, and Masanori Matoba

Journal of Physics: Conference Series 568 022034 (5 pages) 2014.12

Research paper (scientific journal), Joint Work, Last author, Accepted

Enhancement of thermoelectric properties by Se substitution in layered bismuth-chalcogenide LaOBiS_2-xSe_x

Yoshikazu Mizuguchi, Atsushi Omachi, Yosuke Goto, Yoichi Kamihara, Masanori Matoba, Takafumi Hiroi, Joe Kajitani, Osuke Miura

Journal of Applied Physics 116 163915 (4 pages) 2014.10

Research paper (scientific journal), Joint Work, Accepted

The effect of simultaneous substitution on the electronic band structure and thermoelectric properties of Se-doped Co₃SnInS₂ with the Kagome lattice

Masaya Fujioka, Taizo Sibuya, Junya Nakai, Keigo Yoshiyasu, Yuki Sakai, Yoshihiko Takano, Yoichi Kamihara, and Masanori Matoba

Solid State Communications 199 56 - 60 2014.09

Research paper (scientific journal), Joint Work, Last author, Accepted

New phases of binary compounds: CsCl-type RuGe and RuSn

Yuki Sakai, Masanori Matoba, Ikuya Yamada, Kenichi Funakoshi, Takehiro Kunimoto, Yuji Higo, and Yoichi Kamihara

Euro physics letters 107 56003 (6 pages) 2014.09

Research paper (scientific journal), Joint Work, Accepted

Effects of the Cu off-stoichiometry on transport properties of wide gap p-type semiconductor, layered oxysulfide LaCuSO

Yosuke Goto, Mai Tanaki, Yuki Okusa, Taizo Shibuya, Kenji Yasuoka, Masanori Matoba, and Yoichi Kamihara

Applied Physics Letters 105 022104 (4 pages) 2014.07

Research paper (scientific journal), Joint Work, Accepted

From kesterite to stannite photovoltaics: stability and band gaps of the Cu₂(Zn,Fe)SnS₄ alloy

Taizo Shibuya, Yosuke Goto, Yoichi Kamihara, Masanori Matoba, Kenji Yasuoka, Lee A. Burton and Aron Walsh

Applied Physics Letters 104 ( 2 ) 021912 2014.01

Research paper (scientific journal), Joint Work, Accepted

Relations between Superconducting Critical Temperatures and Crystallographic Local Structures in Iron-based Mixed Anion Compounds

Hiromu Shiozawa, Seiya Inagi, Masanori Matoba, Toshiyuki Atou, Mitsuru Itoh, and Yoichi Kamihara

JPS Conference Proceedings: Proceedings of the 12th Asia Pacific Physics Conference (APPC12, Makuhari, Chiba, Japan) 1 012026 (4 pages) 2014.01

Research paper (international conference proceedings), Joint Work, Accepted

Enhanced Thermoelectric Figure of Merit in Stannite–Kuramite Solid Solutions Cu_2+xFe_1-xSnS_4-y (x=0-1) with Anisotropy Lowering

Yosuke Goto, Fumihiko Naito, Rina Sato, Keigo Yoshiyasu, Takanori Itoh, Yoichi Kamihara, and Masanori Matoba

Inorganic Chemistry 52 ( 17 ) 9861-9866 2013.08

Research paper (scientific journal), Joint Work, Last author, Accepted

Ferromagnetic Quantum Critical Point Induced by Tuning the Magnetic Dimensionality of the Heavy-Fermion Iron Oxypnictide Ce(Ru_1-xFe_x)PO

Shunsaku Kitagawa, Kenji Ishida, Tetsuro Nakamura, Masanori Matoba, and Yoichi Kamihara

Journal of the Physical Society of Japan 82 ( 3 ) 033704 (4 pages) 2013.02

Research paper (scientific journal), Joint Work, Accepted

擬二次元格子系であるCeRu1-xFexPOの組成制御を厳密に行い、微視的な磁性と量子臨界点付近の磁気ゆらぎの次元性を31P-NMRより明らかにした。母相 (x = 0)中のCeイオンは、正方格子をとるにも関わらず、状態密度とナイトシフトの相関にょり定義されたスケーリング指数から判断すると、三次元的な強磁性を示す。RuとFeの固溶体では量子臨界点(QCP)付近で三次元的な強磁性秩序から二次元的な強磁性秩序に変化する。

Pressure-induced tetragonal-orthorhombic phase transitions in CeRuPO

Shigeto Hirai, Yoichi. Kamihara, Atsushi Wakatsuki, Masanori Matoba, and Wendy L. Mao

Applied Physics Letters 102 ( 5 ) 051917 (5 pages) 2013.02

Research paper (scientific journal), Joint Work, Accepted

Ferromagnetic quantum critical point in heavy-fermion iron oxypnictide Ce(Ru_1-xFe_x)PO

Shunsaku Kitagawa, Kenji Ishida, Tetsuro Nakamura, Masanori Matoba, and Yoichi Kamihara

Physical Review Letters 109 ( 22 ) 227004 2012.11

Research paper (scientific journal), Joint Work, Accepted

Paramagnetic phase of heavy-fermion compound, CeFePO, probed by ⁵⁷Fe Mossbauer spectroscopy

Tetsuro Nakamura, Takashi Yamamoto, Masanori Matoba, Yasuaki Einaga, Yoichi Kamihara

Journal of Physical Society of Japan 81 ( 5 ) 064714 (4 pages) 2012.05

Research paper (scientific journal), Joint Work, Accepted

Analysis of interdiffusion between SmFeAsO_0.92F_0.08 and metals for ex situ fabrication of superconducting wire

Masaya Fujioka, Masanori Matoba, Toshinori Ozaki, Yoshihiko Takano, Hiroaki Kumakura, and Yoichi Kamihara

Superconductor Science and Technology 24 ( 7 ) 075024- 075029 2011.06

Research paper (scientific journal), Joint Work, Accepted

To ﬁnd good sheath materials that react minimally with the superconducting core of iron-based superconducting wires, we investigated the reaction between polycrystalline SmFeAsO_0.92_F_0.08_ and the following seven metals: Cu, Fe, Ni, Ta, Nb, Cr and Ti. Each of the seven metals was prepared as a sheath-material candidate. The interfacial microstructures of SmFeAsO_0.92_F_0.08_ and these metal-sheath samples were analysed by an electron probe microanalyzer after annealing at 1000◦C for 20 h. Amongst the seven metal-sheath samples, we found that Cu was the best, because it reacted only very weakly with polycrystalline SmFeAsO_0.92_F_0.08_. Moreover, Cu is essential for superconducting wires as a stabilizing material. Metal sheaths made of Fe and Ni do not give rise to reaction layers, but large interdiffusion between these metals and polycrystalline SmFeAsO0.92F0.08 occurs. In contrast, metal sheaths made of Ta, Nb, Cr and Ti do form reaction layers. Their reaction layers apparently prevent electric current from ﬂowing from the sheath material to the superconducting core. In general, through this research, Cu will be expected to be suitable not only as a stabilizing material but also as a sheath material for superconducting Sm-1111 wire fabricated by the ex situ PIT method.

Effective Ex-situ Fabrication of F-Doped SmFeAsO Wire for High Transport Critical Current Density

Masaya Fujioka, Tomohiro Kota, Masanori Matoba, Toshinori Ozaki, Yoshihiko Takano, Hiroaki Kumakura, and Yoichi Kamihara

Applied Physics Express 4 063102 (4 pages) 2011.05

Research paper (scientific journal), Joint Work, Accepted

We demonstrate the fabrication of superconducting SmFeAsO_1-x_F_x_ (Sm-1111) wires by using the ex-situ powder-in-tube technique. Sm-1111 powder and a binder composed of SmF3, samarium arsenide, and iron arsenide were used to synthesize the superconducting core. Although the
F content of Sm-1111 is reduced in the process of ex-situ fabrication, the binder compensates by sufficiently supplementing the F content, thereby preventing a decrease in the superconducting transition temperature and a shrinkage of the superconducting volume fraction. Thus, in the superconducting Sm-1111 wire with the binder, the transport critical current density reaches the highest value of 4 kA/cm^2^ at 4.2 K.

Substitution effect of Ba on magnetic properties of layered oxysulfide (Sr,Ba)₂Cu₂CoO₂S₂ with CoO₂ square planes

Satoshi Okada and Masanori Matoba

Journal of Physics: Conf. Ser. (the 25th International Conference on Low Temperature Physics (LT25)) 150 042154-042157 2009.04

Research paper (scientific journal), Joint Work, Accepted

We have studied the magnetic properties of Ba-doped layered cobalt oxysulfide (Sr,Ba)_2_Cu_2_CoO_2_S_2_ with CoO_2_ squre-planes. The antiferromagnetic nature was considered to originate from the CoO_2_ layer dominantly. However, the effect of the inter-layer of CoO_2_ planes has not been clear. We therefore synthesized polycrystalline (Sr,Ba)_2_Cu_2_CoO_2_S_2_, and investigated the effect of inter-layer distance on the magnetic properties in detail. When Sr was substituted by Ba, the difference between zero-field-cooled and field-cooled magnetization was found to decrease clearly, and such difference was ascribed to reflect the increase of the distance between CoO_2_ layers owing to the difference of the ionic radii between smaller Sr and lager Ba. There is a possibility that two dimensional magnetic order has strengthened.

Thermoelectric Figure of Merit of Anisotropic Bulk Materials in the Presence of Polar Optical Phonon Scattering

Kazuma Ikeda and Masanori Matoba

Japanese Journal of Applied Physics 47 2189-2191 2008.04

Research paper (scientific journal), Joint Work, Accepted

The effect of mass anisotropy on the thermoelectric figure of merit in the presence of polar optical phonon (POP) scattering is numerically studied. Electron transport is considered using the linear Boltzmann transport equation. The mass anisotropy is advantageous for the figure of merit along the principal directions of a small effective mass if phonon thermal conductivity is large. Inelasticity plays an essential role in the obtained result. The result is qualitatively different from that for an ionised impurity model.

Electronic and magnetic nature of shandite-type A₂Co₃S₂ (A=Sn,In)

Atsushi Umetani, Eiji Nagoshia, Takashi Kuboderaa, and Masanori Matoba

Physica B 403 1356-1358 2007.10

Research paper (scientific journal), Joint Work, Accepted

We investigated electronic and magnetic nature of A_2_Co_3_S_2_ (A=Sn,In) to reveal two different characteristics of metallic Co–Sn and strongly correlated electronic Co–S bondings. Co 2p X-ray photoelectron spectroscopy (XPS) shows a complicated and mixed-valence like feature with strong satellite. This origin can be explained by two different characteristics of Co–Sn/Co–S bonding nature. This feature is consistent with characteristic electron-density distributions obtained by the maximum-entropy method (MEM)-based pattern fitting analysis and the LSDA+U band calculation.

Scattering Anisotropy Effect on Layered Thermoelectric Materials

Kazuma Ikeda, Toshihisa Yago, and Masanori Matoba

Japanese Journal of Applied Physics 46 4184-4188 2007.07

Research paper (scientific journal), Joint Work, Accepted

The effect of scattering anisotropy caused by mass anisotropy on the thermoelectric figure of merit is investigated. The simplest electron transport model is considered assuming a single-band, parabolic energy dispersion relation and ionized impurity scattering, which is assumed to be elastic. The wave-vector dependence of the relaxation time is fully considered within the relaxation-time approximation. Transport coefficients are calculated using the anisotropic relaxation time at finite temperatures. The figure of merit perpendicular to the axis with the largest effective mass is shown to decrease as the effective mass ratio increases. This result indicates that the weak confinement of electrons into layers of bulk materials cannot be the direct cause of the enhancement of the figure of merit along the layers.

Mass anisotropic effects on the thermoelectric figure of merit

Kazuma Ikeda, Toshihisa Yago and Masanori Matoba

Proceedings of 25th-International Conference on Thermoelectrics (Vienna, 2006) (25th-International Conference on Thermoelectrics) 293-295 2006.09

Research paper (conference, symposium, etc.), Joint Work, Accepted

Electronic nature of layered oxysulfide Sr_2-xCa_xCu₂CoO₂S₂ with CoO₂ planes

Kana Ito, Taro Endo, Takashi Kubodera, Yoichi Kamihara, Masanori Matoba, and Hijiri Kito

Journal of Applied Physics 99 08F705-08F707 2006.04

Research paper (scientific journal), Joint Work, Accepted

We have studied the electronic nature of the layered oxysulfide Sr_2-x_Ca_x_Cu_2_CoO_2_S_2_ which has strongly correlated CoO_2_ square planes. These materials exhibit narrow-gap semiconducting behavior and the conduction mechanism depends on the temperature. Valence band x-ray photoemission spectroscopy spectra show that Ca doping and the production of Sr defects cause the generation of a quasiparticle band near the Fermi level. These phenomena suggest that the materials are changing from correlated semiconductors to bad metals.

Magnetic properties of Fe_1-xCo_xCr₂S₄

Ryuichiro Noda, Yoichi Kamihara, and Masanori Matoba

Journal of Applied Physics 99 08F712-08F714 2006.04

Research paper (scientific journal), Joint Work, Accepted

We designed a series of samples with Co substitution (Fe_1-x_Co_x_Cr_2_S_4_, 0≦x≦1) and studied the Co doping effect in FeCr_2_S_4_. Spin glass transitions are observed in lower temperature regions and ferrimagnetic transitions are observed in higher temperature regions. The paramagnetic-ferrimagnetic transition temperature (T_C_) increases with the amount of Co substitution. In order to clarify the magnetic character at the transition point, a critical exponent was obtained at about T_C_. The exponent changes from Ising to Heisenberg as x increases.

Ni substitution effect on magnetic and transport properties in metallic ferromagnet Co₃Sn₂S₂

Takashi Kubodera, Hirotaka okabe, Yoichi Kamihara, and Masanori Matoba

Physica B 378-380 1142-1143 2006.02

Research paper (scientific journal), Joint Work, Last author, Accepted

We investigated the magnetic and transport properties of polycrystalline (Co_1-x_Ni_x_)_3_Sn_2_S_2_(0≦x≦1) to ascertain the magnetism of the new metallic ferromagnet Co_3_Sn_2_S_2_. In Co_3_Sn_2_S_2_ magnetization does not saturate up to 5.5 T at 10 K, and the estimated saturation moment (p_s_) is small (0.2μ_B_ per Co atom). In (Co_1-x_Ni_x_)_3_Sn_2_S_2_, the electrical resistivity shows metallic behavior without a hump but has a kink at T_C_. The T_C_ and magnetic susceptibility gradually decrease with increasing x, and there is no antiferromagnetic phase throughout the full range of composition. These results indicate that Co_3_Sn_2_S_2_ is a weak itinerant ferromagnet; while, the same order of the Rhodes–Wohlfarth p_c_/p_s_ value as CoS_2_ suggests the existence of a localized moment.

Low-temperature magnetoresistance of layered cobalt oxides Na_xCoO₂

Hirotaka Okabe, Jun Akimitsu, Takashi Kubodera, Masanori Matoba, Toru Kyomen and Mitsuru Itoh

Physica B 378-380 863-864 2006.02

Research paper (scientific journal), Joint Work, Accepted

We measured transport properties in layered cobalt oxides Na_x_CoO_2_, that are parent materials of the superconductor Na_x_CoO_2_·yH_2_O, in order to reveal so-far unsettled origin of these electronic and magnetic features. Various sodium nonstoichiometric samples Na_x_CoO_2_ (x=0.47,0.62,1.0) have been carefully synthesized to control the carrier density and the electronic state of cobalt ions. We found a large negative magnetoresistance (MR) effect in the vicinity of x~0.5 and 1.0. The x=0.47 and 1.0 samples show negative MR, -45% and -10%, respectively, at 90 kOe and 4 K. These negative MR suggest the pseudogap formation due to the charge ordering in CoO_2_ layers, such as Ca_3_Co_4_O_9_ and Bi2-x_Pb_x_Sr_2_Co_2_O_y_, all of which exhibit similar behaviors. The suppression of the pseudogap by a magnetic field causes the large negative magnetoresistance.

Metal-nonmetal transition in Ge doped spinel-type CuCr₂S₄

Yoichi Kamihara, Masanori Matoba, Toru Kyomen and Mitsuru Itoh

Physica B 378-380 1120-1121 2006.02

Research paper (scientific journal), Joint Work, Accepted

Transport properties of Fe_1-xMn_xCr₂S₄

Yoichi Kamihara, Yukinori Takeshita, Masanori Matoba, Toru Kyomen, and Mitsuru Itoh

Physica B 359-361 1207-1209 2005.05

Research paper (scientific journal), Joint Work, Accepted

FeCr_2_S_4_ has a spin-glass phase below 60K (=T_g_) and a ferrimagnetic phase in the temperature range 60–170K (T_C_=170 K). Mn doping gives an increase of a paramagnetic phase which coexists with a ferrimagnetic phases, and shift of magnetic transition temperature (T_g_=45K, T_C_=130K for Fe_0.5_Mn_0.5_Cr_2_S_4_). The conduction property changes into variable range hopping (VRH) from thermal activated transport below T_g_ for Fe_1-x_Mn_x_Cr_2_S_4_. This conducting transition would be associated with the correlated Fe 3d orbital ordering below T_g_.

Transport Properties and Electronic States in the Layered Thermoelectric Rhodate (Bi_1-xPb_x)_1.8Ba₂Rh_1.9O_y

Satoshi Okada, Ichiro Terasaki, Hirotaka Okabe and Masanori Matoba

Journal of the Physical Society of Japan 74 1525-1528 2005.05

Research paper (scientific journal), Joint Work, Last author, Accepted

Resistivity, thermopower and Hall coefficient have been systematically measured for polycrystalline samples of (Bi_1-x_Pb_x_)_1.8_Ba_2_Rh_1.9_O_y_. An upturn of the resistivity and the Hall coefficient below 50 K is ascribed to decrease in the density of states due to a pseudogap formation. The thermopower and Hall coefficient are nearly identical to those of the thermoelectric oxide Bi_2_Sr_2_Co_2_O_y_. This suggests a nearly identical density of states between the two oxides, which is also verified from a first-principle calculation, where a broader 4d orbital and a larger rhodium-rhodium distance along the in-plane direction accidentally give nearly the same density of states as those of the layered cobalt oxides.

Magnetoresistance in spinel-type Mg_xCu_1-xCr₂S₄

Yoichi Kamihara, Masanori Matoba, Toru Kyomen, and Mitsuru Itoh

Solid State Communications 132 247-251 2004.09

Research paper (scientific journal), Joint Work, Accepted

CuCr_2_S_4_ shows a p-type metallic conductivity and ferromagnetism with Curie temperatures T_c_ of 375 K, and exhibit magnetic anomaly at 84 K (=T_m_). CuCr_2_S_4_ exhibits the coexistence of both the ferromagnetism and spin-glass with the irreversible magnetic effect below T_m_. The partial 20% Mg-substitution for Cu in CuCr_2_S_4_ slightly reduces the T_c_ and T_m_. Magnetorsistance of Mg_x_Cu_1-x_Cr_2_S_4_ can be expressed as Δρ=aH^2^-bH^n^ below T_m_. The parameters a, b, and n are temperature-dependent adjustable parameters. These unique MR behavior would be attributed to the coexistence of the ferromagnetism and spin-glass below T_m_. Mg-substitution decreased the conducting carrier, which forms the conduction band whose orbital motion gave the positive MR contribution. Therefore, Mg-substitution gave smaller positive MR contribution and consequently gave larger negative MR (max. 7% at 10 K) in Mg_0.2_Cu_0.8_Cr_2_S_4_. These results suggest that Cr 3d band filling control can be expected to give functional magnetoelectric transport properties in CuCr_2_S_4_.

Dielectric responses of the layered cobalt oxysulfide Sr₂Cu₂CoO₂S₂ with CoO₂ square planes

Satoshi Okada, Ichiro Terasaki, Hiromasa Ooyama, and Masanori Matoba

Journal of Applied Physics 95 6816-6818 2004.06

Research paper (scientific journal), Joint Work, Last author, Accepted

We have studied the dielectric responses of the layered cobalt oxysulfide Sr_2_Cu_2_CoO_2_S_2_ with the CoO_2_ square planes. With decreasing temperature below the Néel temperature, the resistivity increases like a semiconductor, and the thermopower decreases like a metal. The dielectric constant is highly dependent on temperature, and the dielectric relaxation is systematically changed with temperature, which is strongly correlated to the magnetic states. These behaviors suggest that carriers distributed homogeneously in the paramagnetic state at high temperatures are expelled from the antiferromagnetically ordered spin domain below the Néel temperature.

First-principles study of electronic and magnetic structure in layered cobaltite Na_0.75CoO₂

Hirotaka Okabe, Masanori Matoba, Toru Kyomen, and Mitsuru Itoh

Journal of Applied Physics 95 6831-6833 2004.06

Research paper (scientific journal), Joint Work, Accepted

The electronic structure of Na_0.75_CoO_2_ has been calculated by the LDA+U method, considering the location of Na ions. The magnetic moments of Co ions are strongly influenced by the bond distances between the Co and Na ions, and are unusually distributed. This implies the occurrence of a charge disproportionation state (2Co^+3.25^+Co^+3.25+d^+Co^+3.25–d^) in this material. The magnetic ground state of Na_0.75_CoO_2_ is therefore a spin-glass-like, short-range ordered state resulting from randomly distributed magnetic Co ions.

スピネル型硫化物Fe_1-xMn_xCr₂S₄における巨大磁気抵抗効果

神原陽一，竹下之典, 的場正憲，京免徹，伊藤満

日本応用磁気学会誌 28 347-350 2004.03

Research paper (scientific journal), Joint Work, Accepted

We report the Mn doping eﬀect in FeCr_2_S_4_, which does not possess heterovalency, or static Jahn-Teller distortion, but exhibits large magnetoresistance. In order to see the effects of substituting Fe^2+^ for Mn^2+^ on the conduction, magnetism, and magnetoresistance, we carried out an experimental study of the electrical and magnetic properties of Fe_0.5_Mn_0.5_Cr_2_S_4_. FeCr_2_S_4_ has a spin-glass phase below 60 K (=T_g_) and a ferrimagnetic phase in the temperature range 60-170 K (T_c_ = about 170 K). In Fe_0.5_Mn_0.5_Cr_2_S_4_, both the spin-glass and ferrimagnetic transitions are observed in lower temperature regions (T_g_=45 K, T_c_=140 K). FeCr_2_S_4_ is a semiconductor, but exhibits metallic-like behavior in the temperature range 150-170 K. Fe_0.5_Mn_0.5_Cr_2_S_4_ does not exhibit such metallic behavior, but anomalous transition of the temperature dependence of resistivity is observed in the temperature range 100-180 K. Fe_0.5_Mn_0.5_Cr_2_S_4_ exhibits a larger maximum negative magnetoresistance (MR) than FeCr_2_S_4_. Thses experimental data can be well explained on the basis of the polaron model.

Magnetic Phase Transition in Pd_xCo_yO₂

Hirotaka Okabe, Masanori Matoba, and Mitsuru Itoh

Physica B 329-333 948-949 2003.05

Research paper (scientific journal), Joint Work, Accepted

The nonstoichiometric compound Pd_x_Co_y_O_2_ (x=0.72,y=0.68) were carefully prepared by the metathetical reaction and characterized by the measurements of the powder X-ray diffraction, the inductively coupled plasma spectrum, the DC magnetic susceptibility, and the specific heat. The stoichiometric PdCoO_2_ exhibits Pauli-paramagnetism, while two magnetic phase transitions were indeed observed in Pd_0.72_Co_0.68_O_2_. The deviation of field-cooled from zero-field-cooled curves appears below 55 K, indicating a certain kind of antiferromagnetic phase transition. The well-defined cusp is seen with a peak at T_g_=4.5 K, indicating the existence of spin-glass like transition.

Magnetic property and electronic structure of itinerant Pd_xCo_yO₂ magnets

Hirotaka Okabe, Masanori Matoba, Toru Kyomen, and Mitsuru Itoh

Journal of Applied Physics 93 7258-7260 2003.05

Research paper (scientific journal), Joint Work, Accepted

The electronic structure of the delafossite-type compound PdCoO_2_ is calculated by the full potential linear muffin-tin orbital method and the magnetic property of the composition modified (defect injection introduced) compound Pd_0.72_Co_0.68_O_2_ was investigated. The calculation reveals that the density of states of PdCoO_2_ around the Fermi level is mainly composed of Pd 4d and Co 3d and O 2p orbitals, and the Fermi level is located just at the depression of the density of states. The magnetic nature of the composition modified Pd_0.72_Co_0.68_O_2_ compound is quite complex. The slow spin dynamics found below T_f_ can be interpreted by considering that the weak ferromagnetic moment in each CoO_6_ plane is itself disordered. This behavior is explained by the short-range character of the randomness which leads to a finite-size magnetized cluster, and suggests that the presence of these clusters would induce a spin-glass like feature for T<T_f_.

Doping effect on transport properties of layered oxysulfide Sr₂Cu₂CoO₂S₂ with CoO₂ square planes

Satoshi Okada, Hirotaka Okabe and Masanori Matoba

Physica B 329-333 916-917 2003.05

Research paper (scientific journal), Joint Work, Last author, Accepted

Layered cobalt oxysulfide Sr_2_Cu_2_CoO_2_S_2_ crystallizes in an unusual intergrowth structure which represents a combination of SrCu_2_S_2_ and SrCoO_2_. Sr_2_Cu_2_CoO_2_S_2_ is a p-type antiferromagnetic semiconductor with T_N_(=200 K). And below T_t_(=125 K), the antiferromagnetic nature is changed from 2D to 3D. We studied Seebeck coefficient of Sr_2_Cu_2_CoO_2_S_2_ and its Cu-doped compounds. Their Seebeck coefficients near Tt tend to enhance by the Cu-doping into CoO_2_ square planes. The curves of the temperature dependence of Sr_2_Cu_2_Cu_x_Co_1-x_O_2_S_2_ is changed near T_N_, and the change points shift to high temperature by Cu-doping. The behavior resembles in TN shift of the magnetic property. The transport properties of Cu-doped Sr_2_Cu_2_CoO_2_S_2_ is affected by their magnetism.

層状Mn酸化硫化物Sr₂CuMnO₃S及びSr₄Cu₂Mn₃O_7.5S₂における不純物置換効果

神原陽一, 長沼順子，安仲健太郎，石井守，上野広伸，的場正憲

日本応用磁気学会誌 27 666-669 2003.04

Research paper (scientific journal), Joint Work, Last author, Accepted

Sr_4-x_La_x_Cu_2_Mn_3_O_7.5_S_2_ with alternating Cu_2_S_2_ and perovskite oxide layers have been synthesized and characterized. The perovskite oxide layers in Sr_2_CuMO_3_S (M=Fe and Ga) and A_4_Cu_2_Mn_3_O_7.5_S_2_ (A=Sr and La) have the stacking sequence with -MO_2_-SrO-SrO-MO_2_- and -MnO_2_-AO-Mn_1.5_-AO-MnO_2_-, respectively. Sr_2_CuFe_1-x_Ga_x_O_3_S (x=0, 0.05) is semiconducting. The electrical resistivity of the x=0.05 sample is ten times lower than that of the x=0
sample, indicating that the conduction path is in Ga-introduced iron oxide layer. Sr_4_Cu_2_Mn_3_O_7.5_S_2_ exhibits a phase transition from paramagnetic to antiferromagnetic states below 100K. In
Sr_4-x_La_x_Cu_2_Mn_3_O_7.5_S_2_ (x=0, 0.1, 0.2, 0.4),
the lattice parameters a and c decerease with increasing x. All samples are semiconducting. The electrical resistivity is lowered with increasing x; that of the x=0.4 sample is one-hundred times lower than
that of the x=0 sample.

Magnetic properties of novel layered oxysulfide Sr₂Cu₂(Co,Cu)O₂S₂ with Cu-doped CoO₂ square-planes

Satoshi Okada, Masanori Matoba, Yoichi Kamihara, Tadamasa Takeuchi, Satoshi Fukumoto, Shunji Soyano, Hajime Yoshida, Kenji Ohoyama, and Yasuo Yamaguchi

Journal of Applied Physics 91 8861-8863 2002.08

Research paper (scientific journal), Joint Work, Accepted

We have studied the magnetic properties of layered oxysulfide Sr_2_Cu_2_(Co,Cu)O_2_S_2_ with the (Co,Cu)O_2_ planes. Magnetic susceptibility shows a broad maximum indicative of two-dimensional antiferromagnetic nature above 140K. Below 80K, the divergence between zero-field cooled and field cooled magnetizations is seen; long time decay is observed at 10 and 75K, while it is not observed at 45K. These feature is discussed from the viewpoint of the strongly and frustrated spin system which is different from the traditional spin glass.

Magnetic and electronic nature of novel layered manganese oxysulfide Sr₂CuMnO₃S

Yoichi Kamihara, Masanori Matoba, Toru Kyomen, and Mitsuru Itoh

Journal of Applied Physics 91 8864-8866 2002.08

Research paper (scientific journal), Joint Work, Accepted

We have synthesized and investigated the magnetic and electronic nature of layered manganese oxysulfide Sr_2_CuMnO_3_S which crystallizes in an unusual intergrowth structure with Cu_2_S_2_ and pyramidal MnO_5_ layers separated by Sr ions. A Cu 2p x-ray photoemission spectroscopy (XPS) spectrum of Sr_2_CuMnO_3_S indicates that the Cu ion is in the monovalent state, or Cu^+^. This feature of the Mn 2p XPS spectrum of Sr_2_CuMnO_3_S is similar to that of the parent compound La^3+^Mn^3+^O_3_ of colossal magnetoresistance materials. The MnO_5_ cluster model analysis suggests that the electronic nature of the pyramidal MnO_5_ layers belongs to a strongly correlated electron system, and the system is the so-called Mott insulator resulting from the strongly correlated electron nature. Magnetic susceptibility exhibits low-dimensional antiferromagnetic ordering of Mn^3+^ in pyramidal MnO_5_ layers. Fitting the data to Curie–Weiss law provides the evidence of strong second neighbor Mn–Mn interaction.

Pressure effect on magnetic nature of Sr₂Cu₂CoO₂S₂ with strongly correlated CoO₂ square-planes

Satoshi Okada, Masanori Matoba, Hajime Yoshida, Kenji Ohoyama, and Yasuo Yamaguchi

Journal of Physics and Chemistry of Solids 63 983-985 2002.08

Research paper (scientific journal), Joint Work, Accepted

We have studied pressure effects on the magnetic and electronic nature of layered oxysulfide Sr_2_Cu_2_CoO_2_S_2_ which crystallizes in an unusual intergrowth structure. The derivative permeability dμ/dT curves have a kink near T_t_ at which the antiferromagnetic nature is changed from 2D to 3D; T_t_ extremely rises with increasing pressure (dT_t_/dP=13.5 K/kbar), indicating that 3D antiferromagnetic state is more stable under pressure. The T_t_ in the dμ/dT curves correspond to the bending point of the resistivity, and above T_t_ the nearest-neighbor hopping conduction occurs. These features would be discussed from the viewpoint of the coupled nature of charge carriers and 2D antiferromagnetic spin ordering.

Magnetic Anomalies in Na_xCoO₂ (x=0.75)

Tadamasa Takeuchi, Masanori Matoba, Tomoko Aharen, and Mitsuru Itoh

Physica B 312-313 719-720 2002.07

Research paper (scientific journal), Joint Work, Accepted

Magnetic Dilution and Electronic Nature in La_0.7Pb_0.3Mn_1-yZn_yO₃

Tadahiko Kanoh and Masanori Matoba

Journal of Physics and Chemistry of Solids 63 252 2002.07

Research paper (scientific journal), Joint Work, Accepted

We have studied the magnetic dilution and electronic nature of Zn doping on the Mn site in the colossal magnetoresistant material La_0.7_Pb_0.3_MnO_3_ (x≦0.3). Small non-magnetic Zn^2+^ doping tends to separate the system into ferromagnetic clusters to weaken the long-range ferromagnetic order and to reduce the Curie temperature. The spin polarizability of the x=0〜0.3 samples is estimated to be 0.97〜1.00, indicating that the x=0〜0.3 samples are the spin polarized materials in which the conductivity is dominated by single-spin charge carriers. Small doping (x≧0.1) induces the metal–insulator transition and destroys the metallic state with long-range ferromagnetic order.

新規な無機ハイブリッド型層状遷移金属硫化酸化物ペロブスカイト関連酸化物Sr₂Cu(Fe,Ga)O₃S および(Sr,La)₄Cu₂Mn₃O_7.5S₂の合成と評価

長沼順子, 神原陽一，的場正憲

日本応用磁気学会誌 26 376-379 2002.04

Research paper (scientific journal), Joint Work, Accepted

層状Mn酸化硫化物Sr₂CuMnO₃Sの物性

神原陽一, 岡田悟志, 的場正憲

日本応用磁気学会誌 26 372-375 2002.04

Research paper (scientific journal), Joint Work, Accepted

La_0.7Pb_0.3Mn_1-zZn_yO₃における金属－非金属転移とZnによる磁気希釈

加納忠彦, 神原陽一，的場正憲

日本応用磁気学会誌 26 368-371 2002.04

Research paper (scientific journal), Joint Work, Accepted

Magnetism of Novel Layered Cobalt Oxysulfide Sr₂Cu₂CoO₂S₂ with Strongly Correlated CoO₂ Square-Planes

Masanori Matoba, Tadamasa Takeuchi, Satoshi Okada, Yoichi Kamihara, Mitsuru Itoh, Kenji Ohoyama, and Yasuo Yamaguchi

Physica B 312-313 630-631 2002.03

Research paper (scientific journal), Joint Work, Accepted

Magnetic and electronic nature have been investigated for the novel layered oxysulfide Sr_2_Cu_2_CoO_2_S_2_ (space group I/4mmm). Sr_2_Cu_2_CoO_2_S_2_ is the antiferromagnet with T_N_ (=200 K) determined by the measurements of neutron powder diffraction and magnetic susceptibility (χ). The dχ/dT shows a broad maximum indicative of two-dimensional antiferromagnetic nature, which is not originated from the (Cu^+^S)_2_ layers but the strongly correlated Co^2+^O_2_ square-planes revealed by the X-ray photoemission spectroscopy.

Magnetism of Novel Layered Cobalt Oxysulfide Sr₂Cu₂CoO₂S₂ in Strongly Correlated Electron Systems

Masanori Matoba, Kenji Ohoyama, and Yasuo Yamaguchi

Workshop on Studies of Structures in Magnetic Compounds by Neutron Diffraction Technique 2001 2001 11-13 2001.12

Research paper (conference, symposium, etc.), Joint Work

Magnetic nature has been investigated for the novel ayered oxysulfide Sr_2_Cu_2_CoO_2_S_2_ which crystallizes in an unusual intergrowth structure with alternating square-planar CoO_2_ planes and anti-PbO type Cu_2_S_2_ layers. Sr_2_Cu_2_CoO_2_S_2_ is the strongly correlated antiferromagnet with T_N_ (=200K) obtained from measurements of the magnetic contribution d(χT)/dT. Below 80K(=T_1_), the difference between ZFC and FC magnetic susceptibilities are observed, indicating that Sr_2_Cu_2_CoO_2_S_2_ exhibits a spin-glass-like (spin-frustrated) transition. Above 200K(=T_2_), magnetic susceptibility shows a broad maxium indicative of 2D antiferromagnetic coupling in the square-planar CoO_2_ planes. From the NPD HERMES experiment, below 200K(=T_2_) we have confirmed the occurrences of new additional reflection peaks, which can be indexed on the K_2_NiF_4_-type magnetic cell and can be therefore assigned to the square-planar CoO_2_ planes with antiferromagnetic ordering. The magnetic reflection peaks are clearly seen in the NPD pattern at 75K in the spin-glass-like (spin-frustrated) region, indicating a possibility that Sr_2_Cu_2_CoO_2_S_2_ is the unusual spin-glass-like material.

多元系層状磁性半導体Sr₂Cu₂Zn_1-xMn_xO₂S₂の物性

神原陽一, 岡田悟志, 的場正憲

日本応用磁気学会誌 25 739-742 2001.12

Research paper (scientific journal), Joint Work, Accepted

Neutron Powder Diffraction on Novel Layered Cobalt Oxysulfide Sr₂Cu₂CoO₂S₂ in Strongly Correlated Electron Systems

Masanori Matoba, Kenji Ohoyama, Shunji Soyano, Satoshi Fukumoto, and Yasuo Yamaguchi

Journal of the Physical Society of Japan 70 Suppl. A64-66 2001.07

Research paper (scientific journal), Joint Work, Accepted

Electronic structure of delafossite-type AgMO₂ (M=Fe, Co, Ni) studied by the cluster model analysis

Masanori Matoba, Hironobu Ueno, Hirotaka Okabe, and Mitsuru Itoh

Proceedings of the fourth Pacific Rim International Conferences on Advanced Materials and Processing (Hawaii, 2001) 2119-2120 2001.04

Research paper (conference, symposium, etc.), Joint Work, Accepted

Transport properties and electronic nature of delafossite-type PdCoO₂ and its related compounds

Hirotaka Okabe, Masanori Matoba, and Mitsuru Itoh

Proceedings of the fourth Pacific Rim International Conferences on Advanced Materials and Processing (Hawaii, 2001) 2117-2118 2001.04

Research paper (conference, symposium, etc.), Joint Work, Accepted

ペロブスカイト関連酸化物Sr₃(Ga_1-xMn_x)₂O₆ (0≦x≦0.2)の結晶構造と磁性

長沼順子, 的場正憲

日本応用磁気学会誌 25 719-722 2001.04

Research paper (scientific journal), Joint Work, Accepted

Cu-Substitution Effect on a Square-Planar CoO₂ Layer in a New Layered Transition-Metal Oxysulfide Sr₂Cu₂CoO₂S₂

Masanori Matoba, Satoshi Okada, Satoshi Fukumoto, Shunji Soyano, and Hijiri Kito

Japanese Journal of Applied Physics 39 498-500 2000.11

Research paper (scientific journal), Joint Work, Accepted

Optical study of the metal-nonmetal transition in Ni_1-δS

Hideaki Okamura, Jun Naitoh, Takao Nanba, Masanori Matoba, Masaya Nishioka, Shuichiro Anzai, Iwao Simomura, Kazutoshi Fukui, Hiroshi Miura, Hideyuki Nakagawa, Kazumichi Nakagawa, and Toyohiko Kinoshita

Solid State Communications 112 91-95 1999.09

Research paper (scientific journal), Joint Work, Accepted

Optical reflectivity spectra of the hexagonal Ni_1-δ_S have been measured to study its electronic structures, in particular those associated with the metal–nonmetal transition in this compound. Samples with δ=0.002 and 0.02 are studied, which have transition temperatures T_t_ = 260 K and 150 K, respectively. Upon the transition, a pronounced dip appears in the infrared region of the reflectivity spectra. The optical conductivity spectra suggest that the nonmetallic phase is a carrier-doped semiconductor with an energy gap of 0.2–0.3 eV. The spectra also show that the gap becomes larger with decreasing temperature, and smaller with increasing . It is found that the overall spectrum in the nonmetallic phase can be explained in terms of a charge-transfer semiconductor, consistent with recent theoretical and photoemission studies of NiS.

Pressure Effect on the Curie Temperature of (Mn_1-zFe_z)₇Sn₄

Shuichiro Anzai, Seiji Fujii, Satoru Ohta, Hajime Yoshida, Takejiro Kaneko, Ryuichi Sugi, Takayuki Yoshida, Masanori Matoba and Tomohiko Wada

The Review of High Pressure Science and Technology 7 547-549 1998.07

Research paper (scientific journal), Joint Work, Accepted

Magnetic susceptibility, thermoelectric power, electrical resistivity study of the nonmetal-metal transition in (Ni_1-xV_x)_0.98S

Masaya Nishioka, Teruki Motohashi, Masanori Matoba, Mitsuo Mikami, and Shuichiro Anzai

Physica B 237-238 151-153 1997.08

Research paper (scientific journal), Joint Work, Accepted

Long-Time Decay of Thermoremanent Magnetization through Stepwise Changes of the Reentrant Spin-Glass-Like State in the Ni₂In-Type Mn₇Sn₄

Yoshihiro Isogai, Takashi Kobayashi, Takayuki Yoshida, Shuichiro Anzai, and Masanori Matoba

Physica Status Solidi b 203 213-220 1997.08

Research paper (scientific journal), Joint Work, Accepted

The zero-field-cooled magnetization at the magnetic field H = 300 Oe shows anomolous kinks at TA and TB (>TA far below the reentrant spin-glass-like transition temperature Tf (above which a long-range ferrimagnetic ordering is set up). The irreversibility between the zero-field-cooled and the field-cooled magnetizations, and the time decay of the thermoremanent magnetization (TRM) are observed below the ferrimagnetic Curie temperature TC. The decay feature can be described by Ogielski's power law TRM = At - whose exhibits peaks at TA, TB, Tf and TC. The peak of at TC can be fitted by the combination of Ising type and Ginzburg-Landau type expressions. Three stepwise changes of the spin-glass-like state below Tf and the feature of the coexistence of short-range spin-glass and long-range magnetic ordering components above Tf are discussed.

Single Hole Dynamics in the CuO₂ Plane at Half Filling

Johannes J. M. Pothuizen, Robert Eder, Nguyen T. Hien, Masanori Matoba, Alois A. Menovsky and George A. Sawatzky

Physical Review Letters 78 717-720 1997.01

Research paper (scientific journal), Joint Work, Accepted

We present a k-dependent study of the single hole states in Sr_2_CuO_2_Cl_2_. We demonstrate that the controversial "1 eV peaks" in the high Tc's are quasi-particles derived from the same O 2p states as the Zhang-Rice (ZR) singlets, but of different symmetry and intensity in those regions of the Brillouin zone where the hybridization with the correlated Cu 3d states vanishes by symmetry. We use this new source of information to estimate the quasiparticle weight of the ZR singlets, discuss the quasiparticle line shape, and suggest a strong k dependence of the self-energy.

X-Ray Photoemission Spectra of S 2s Core Level in the Charge-Transfer Type Mixed Metallic System (Co_1-xNi_x)_0.91S

Shuichiro Anzai, Teruki Motohashi, Keiso Hayashi, Masanori Matoba, and Atsushi Fujimori

Journal of the Physical Society of Japan 65 2724-2725 1996.08

Research paper (scientific journal), Joint Work, Accepted

Pressure Effect on the Magnetic Transition Temperatures of Ni₂In-Type (Mn_1-uCo_u)₇Sn₄

Takayuki Yoshida, Hajime Yoshida, Ryoichi Sugi, Yoshihiro Isogai, Naoya Tokiwa, Shuichiro Anzai, Masanori Matoba, Takejiro Kaneko, Shunya Abe, and Satoru Ohta

Journal of the Physical Society of Japan 65 1511-1512 1996.08

Research paper (scientific journal), Joint Work, Accepted

X-Ray Photoemission Spectroscopic Study on the Electronic States in the Mixed System between Charge-Transfer and Mott-Hubbard Type Metals : Co_0.91S and V_0.91S

Teruki Motohashi, Keiso Hayashi, Masanori Matoba, Shuichiro Anzai and Atsushi Fujimori

Journal of the Physical Society of Japan 65 1312-1316 1996.08

Research paper (scientific journal), Joint Work, Accepted

In order to study the change of the electronic states from the charge-transfer(CT) type metal to the Mott-Hubbard (MH) one, X-ray photoemission spectra are measured on the NiAs-type (Co_1-x_V_x_)_0.91_S (x ≤ 0.50) and V_0.91_S. The asymmetry parameter α for S 2s and 2p core level spectra decrease with increasing x. This result indicates that the local density of states of S atoms at the Fermi level decreases as x increases; the system changes from the CT-type metal to the MH-one with x. The change in V 2p line shape with x suggests the possibility of the considerable hybridization between V 3d and S 3p in (Co_1-x_V_x_)_0.91_S at lower x region. This feature would be related to the appearance of the extra peak at binding energy E_B_ = 2-3 eV in the valence band X-ray photoemission spectra.

Metal-Nonmetal Transition in NiAs-Type Ni-Fe-S Compound : X-Ray Photoemission Spectroscopic Study

Masanori Matoba, Teruki Motohashi, Kunihiko Shimoda, Hikaru Tamura, Shuichiro Anzai and Atsushi Fujimori

Crystal Research and Technology 31 563-567 1996.08

Research paper (scientific journal), Joint Work, Accepted

The inclusion of charge transfer to the conduction band in a cluster model analysis of some 3d transition metal chalcogenides

A. E. Bocquet, Takashi Mizokawa, Kazutoshi Mamiya, Atsushi Fujimori, Masanori Matoba, Shuichiro Anzai, Shigemasa Suga, and Tomonao Miyadai

Journal of Electron Spectroscopy and Related Phenomena 78 111-114 1996.05

Research paper (scientific journal), Joint Work, Accepted

Photoemission Study of Itinerant Ferromagnetic Cr_1-δTe

Kenya Shimada, Tomohiko Saitoh, Hirofumi Namatame, Atsushi Fujimori, Setsuro Ishida, Shoji Asano, Masanori Matoba, and Shuichiro Anzai

Physical Review B 53 7673-7683 1996.03

Research paper (scientific journal), Joint Work, Accepted

The electronic structures of the itinerant ferromagnets Cr_1-x_Te (x=0.05, 0.25, and 0.375) have been studied by photoemission spectroscopy. The valence-band spectra are compared with the density of states given by band structure calculations. In spite of the itinerant nature of the d electrons, disagreement between the photoemission spectra and the band-structure calculations exists in the magnitude of the d-band exchange splitting and the spectral weight at the Fermi level and 2–4 eV below it: The occupied d band for x=0.05 is shifted away from the Fermi level; the observed spectral weight at the Fermi level is significantly suppressed compared with the band structure calculations for x=0.05 and 0.375, where the nominal d-electron numbers are close to integers 4 and 3, respectively. Configuration-interaction cluster-model calculations have been made for x=0.05 and 0.375 to explain the spectral weight distribution in the high-binding-energy (2–4 eV) region in terms of electron-correlation effects. The d-d on-site Coulomb energy is estimated to be significant, U=2 eV, and nearly equal to or smaller than the charge-transfer energy Δ=2–3 eV.

Effect of charge transfer to the conduction band within a single-impurity model on tne Ni 2p core level line shapes of Ni compounds

A. E. Bocquet, Takashi Mizokawa, Kazutoshi Mamiya, Atsushi Fujimori, Masanori Matoba, Shuichiro Anzai and Shigemasa Suga

Physical Review B 52 13838-13849 1995.11

Research paper (scientific journal), Joint Work, Accepted

We have extended the single-impurity cluster model to include the effects of charge transfer to the conduction band. It is found that these effects can have a considerable influence on the line shapes of core-level spectra of small-gap transition-metal compounds. Using a few additional, well-defined parameters to describe the interactions between the local cluster and the conduction band, and retaining the original intracluster parameters from previous single-impurity models, we find an improved agreement for the Ni 2p spectrum of NiS. The asymmetric line shape is well reproduced, keeping the correct satellite to main peak ratio, which is not possible using the three-peak structure of previous models. The new model is less successful in explaining effects beyond standard single-impurity models in more ionic compounds, such as the double-peak stucture of the main line of the core-level spectrum of NiO, where the interactions between the metal d site and the conduction band are expected to play a lesser role.

Effect of Co Substitution on the Magnetic Properties of the Ni₂In-Type Mn₇Sn₄

Naoya Tokiwa, Tkayuki Yoshida, Toshihiko Shimomura, Ryoichi Sugi, Masanori Matoba, and Shuichiro Anzai

Physica Status Solidi b 189 K33-K36 1995.08

Research paper (scientific journal), Joint Work, Accepted

Effect of 4d Transition Metal Rh Doping on Thermoelectric Power, Magnetic Susceptibility, Thermal Expansion and X-ray Photoemission Spectra in the Charge-Transfer Type Nonmetallic State of NiS

Hideya Ikoma, Masanori Matoba, Mitsuo Mikami and Shuichiro Anzai

Journal of the Physical Society of Japan 64 2600-2608 1995.08

Research paper (scientific journal), Joint Work, Accepted

We report the following two remarks of the Rh impurity effect on the charge-transfer (CT) type nonmetallic state (below the nonmetal-metal transition temperature: T_t_) of 3d transition metal compound NiS. (1) Although the nearest neighbouring M-M (Ni or Rh) and S-S distances increase with increasing x, dT_t_/dx<0. The Rh substitution gives a broad peak with the Fermi edge. A positive sign of T-linear contribution of the thermoelectric power turns to negative one at the critical concentration (x_c_) in Ni_1-x_Rh_x_S. Below T_t_, a Curie constant is observed and increases with increasing x. It is suggested that an impurity band introduced by the Rh atoms leads a change of the electronic state of Ni atoms and the suppression of the CT gap. (2) An empirical relation (dT_t_/dC_N_ >0) is found on Ni_1-x_Rh_x_S, Ni_1-δ_S and NiS_1-y_Se_y_, where C_N_ is the phonon-drag coefficient. The slope dT_t_/dC_N_ becomes smaller in Ni_1-x_M_x_S with the early 3d transition metal impurities (M: Ti, V and Cr).

Electronic Effect of Mn Addition (y) on the Magnetic Properties of the Ni₂In-Type Mn_7+ySn₄

Ryoichi Sugi, Toshiaki Shimomura, Masanori Matoba, Shingo Matsuzaka, Seiji Fujii, Naoto Hagiwara and Shuichiro Anzai

Physica Status Solidi b 189 K65-K68 1995.08

Research paper (scientific journal), Joint Work, Accepted

The inclusion of charge-transfer to the conduction band in a cluster model analysis of core level line shapes

A. E. Bocquet, Takashi Mizokawa, Kazutoshi Mamiya, Atsushi Fujimori, Masanori Matoba, Shuichiro Anzai and Shigemasa Suga

Journal of Physics, Condensed Matter 7 L411-L416 1995.05

Research paper (scientific journal), Joint Work, Accepted

We have extended the single-impurity cluster model to include the effects of charge transfer to the conduction band for the interpretation of the core level photoemission spectra of highly correlated, small-gap semiconducting and metallic transition metal compounds. The model includes the charge fluctuations between the local transition metal site and the conduction band and has been successfully applied to reinterpret the spectra of some 3d transition metal chalcogenides, reproducing well the large asymmetry of the main peaks, as well as the other satellite structures.

Opening of a Correlation-Induced Band Gap in NiS

Motohiko Nakamura, Akira Sekiyama, Hirofumi Namatame, Atsushi Fujimori, Akira Misu, Hideya Ikoma, Masanori Matoba and Shuichiro Anzai

Physical Review Letters 73 2891-2894 1994.11

Research paper (scientific journal), Joint Work, Accepted

We have measured high-resolution photoemission spectra of NiS, which undergoes a nonmetal-metal transition at Tt~260 K. Below Tt, a small band gap opens; the band edge is essentially a step function broadened only by ~ 15 meV. This observation is difficult to reconcile with one-electron band theory, which predicts a much broader band edge, implying a dramatic influence of electron correlation on quasiparticle excitations and on the opening of a band gap in 3D antiferromagnetic insulators.

半導体Cu₄(Sn_1-xGe_x)S₄の熱電能

杉野哲也, 田口直文, 的場正憲, 安西修一郎

日本材料科学会誌 31 130-132 1994.09

Research paper (scientific journal), Joint Work, Accepted

Effect of Early Transition-Metal (M=Ti, V and Cr) Doping on the Electronic Structure of Charge-Transfer Type Compound NiS Studied by Thermoelectric Power and X-Ray Photoemission Measurements

Masanori Matoba, Shuichiro Anzai and Atsushi Fujimori

Journal of the Physical Society of Japan 63 1429-1440 1994.07

Research paper (scientific journal), Joint Work, Accepted

The M 2p core-level XPS peaks of doped elements in Ni1-xMxS are observed at the binding energies of M in “M2S3” rather than those of “MS” below and above the nonmetal-metal transition temperature (T t), indicating that the M atom are ionized to M3+ and acts as shallow donor impuritites. Below T t the T1/2 contribution with negative sign to the thermoelectric power (S) is superimposed on the usual degenerate semiconductive contribution with positive sign. It overcomes the latter contribution above a concentration (x c). The value of x c increases in the order of M=Ti, V and Cr. These results indicate that the T1/2 contribution to S comes from variable range hopping through the localized states formed near E F within the narrow charge-transfer gap of the parent NiS. Above T t the sign of S is negative in the electron-doped Ni1-xMxS as well as in the hole-doped Ni1-xS, suggesting that they have the Fermi surface topology.

強相関電子系NiSの電子構造と磁気的電気的性質：不純物ドーピングによる物性制御要因の探求

的場正憲

平成６年度東北大学金属材料研究所報告 83-105 1994

Research paper (other academic), Single Work

Pressure Effect on the Magnetic Transition Temperatures of Mn₇Sn₃Ge and Mn₇Sn₂Ge₂

Satoru Ohta, Naoto Hagiwara, Seiji Fujii, Hajime Yoshida, Takejiro Kaneko, Shuichiro Anzai and Masanori Matoba

Japanese Journal of Applied Physics 32-3 266-268 1994

Research paper (scientific journal), Joint Work, Accepted

Magnetic Properties of Cr₂RhSe₄ and CrRh₂Se₄

Shuichiro Anzai, Masaaki Ohji, Satoru Ohta, Tetsuya Matsukami, Kiyoshi Sonokawa and Masanori Matoba

Japanese Journal of Applied Physics 32-3 311-312 1994

Research paper (scientific journal), Joint Work, Last author, Accepted

X-Ray Absorption Study of the Metal-Nonmetal transition in NiS and Ni_1-xM_xS (M=Fe and Co)

Motohiko Nakamura, Hirofumi Namatame, Atsushi Fujimori, Maurizio Sacchi, John C. Fuggle, Akira Misu, Takeshi Mamori, Hikaru Tamura, Masanori Matoba, and Shuichiro Anzai

Japanese Journal of Applied Physics 32-3 306-307 1994

Research paper (scientific journal), Joint Work, Accepted

Photoemission Study of the Electronic Structure of the Ferromagnetic Cr_1-δTe System

Kenya Shimada, Tomohiko Saitoh, Hirofumi Namatame, Atsushi Fujimori, Masanori Matoba, Kazuo Hatakeyama and Shuichiro Anzai

Japanese Journal of Applied Physics 32-3 355-356 1994

Research paper (scientific journal), Joint Work, Accepted

Metal-nonmetal transition in NiS induced by Fe and Co substitution: X-ray absorption spectroscopic study

Motohiko Nakamura, Atsushi Fujimori, Maurizio Sacchi, John C. Fuggle, Akira Misu, Takeshi Mamori, Hikaru Tamura, Masanori Matoba and Shuichiro Anzai

Physical Review B 48 16942-16947 1993.12

Research paper (scientific journal), Joint Work, Accepted

In order to reveal the microscopic origin of the metal-nonmetal transition in NiS, we have studied the Ni 2p x-ray-absorption spectra of substituted systems Ni_1-x_M_x_S (M=Fe,Co), whose transition temperature T_t_ varies from 500 K (Ni_0.5_Fe_0.5_S) to below 4 K (Ni_0.94_Co_0.06_S). Spectra taken at room temperature have been analyzed using a configuration-interaction cluster model to deduce changes in the electronic structure parameters, namely, the S-3p-to-Ni-3d charge-transfer energy Δ and the Ni3d –S3p transfer integral T. We find that Fe substitution does not increase the local Ni-S distance as would be expected from the lattice parameters but affects energy levels as is reflected in Δ. The changes in Δ and T derived from the cluster-model analysis explain the increase in the charge-transfer-type band gap in Ni_1-x_Fe_x_S and hence the increase in T_t_ within the cluster model, whereas they do not explain the decrease in T_t_ in Ni_1-x_Co_x_S. In order to explain the dramatic decrease in T_t_ with Co substitution, we propose that the Ni3d–Co3d hybridization increases the bandwidths leading to the closure of the band gap.

X-Ray Absorption Study of the Metal-Nonmetal transition in NiS and Ni_1-xCo_xS

Motohiko Nakamura, Hirofumi Namatame, Atsushi Fujimori, Maurizio Sacchi, John C. Fuggle, Akira Misu, Takeshi Mamori, Hikaru Tamura, Masanori Matoba and Shuichiro Anzai

Photon Factory Activity Report 11 26 1993

Research paper (other academic), Joint Work

Effect of Ge Substitution on the Magnetic Transition Temperature in the Ni₂In-Type Mn₇(Sn_1-xGe_x)₄

Shuichiro Anzai, Naoto Hagiwara, Seiji Fujii, Shinji Kameyama, Masanori Matoba, Takejiro Kaneko, Hajime Yoshida and Satoru Ohta

Physica Status Solidi b 177 K13-K16 1993

Research paper (scientific journal), Joint Work, Accepted

A Spin-Glass-Like State in the Ni₂In-Type Mn₇(Sn_1-xGe_x)₄ below the Ferrimagnetic State

Naoto Hagiwara, Masanori Matoba, Seiji Fujii and Shuichiro Anzai

Physica Status Solidi b 176 K71-K74 1993

Research paper (scientific journal), Joint Work, Accepted

X-Ray Photoemission Spectroscopy Study of Impurity Effect and d-Band Formation Induced by the Substituted 4d Transition Metal Atoms in Ni_1-xRh_xS

Takeshi Mamori, Masanori Matoba, Shuichiro Anzai and Atsushi Fujimori

Journal of the Physical Society of Japan 62 1031-1036 1993

Research paper (scientific journal), Joint Work, Accepted

The effect of Rh substitution on the electronic structure of charge transfer type compound NiS is studied by XPS. We find the following results. (1) A narrow band is newly superimposed on the main peak (d^8^L) of NiS in the valence band region and its width increases with x. (2) The peak position and the line shape of Rh 3d core level spectra are very close to that of Rh metal. (3) The S 2s and the S 2p_3/2_ core level peaks shift toward higher binding energy (E_B_) with increasing x. (4) The Ni 2p_3/2_ core level main peak (d^9^L) shifts toward lower E_B_ with increasing x. (5) The E_B_ separation of the Ni 2p_3/2_ main and satellite peaks decreases as x increases, while the relative intensity of the latter peak to the former one increases. We suggest a tentative model that a Mott-Hubbard type metallic d-band is superimposed on charge transfer type host NiS, and that this contribution is one of the electronic origin for dT_t_/dx<0 reported previously. The origin of the metallic band is attributed to the Rh-Rh and/or Ni-Rh interactions in Ni_1-x_Rh_x_S.

Photoemission Study of the Electronic Structure of the Ferromagnetic Cr_1-δTe System

Kenya Shimada, Tomohiko Saitoh, Hirofumi Namatame, Atsushi Fujimori, Masanori Matoba, Kazuo Hatakeyama and Shuichiro Anzai

Activity Report of Syncrotron Radiation Laboratory 1993 46-47 1993

Research paper (other academic), Joint Work

Co Substitution Effect on the Electronic Structure of NiS Studied by X-Ray Photoemission Spectroscopy

Takeshi Mamori, Masanori Matoba, Atsushi Fujimori and Shuichiro Anzai

Journal of the Physical Society of Japan 61 433-436 1992

Research paper (scientific journal), Joint Work, Accepted

X-ray photoemission spectroscopy (XPS) measurements of the valence band, Ni 2p core level, Co 2p core level and S 2s, 2p core levels were carried out on the metallic state of Ni1-vCovS (0≤ v≤ 0.06). The main peak of the valence band spectra shifts toward lower binding energy (E B) with increasing v ( dE B/ dv=-2.6± 0.4 eV/mol). This behavior is different from those reported on vacancy introduction or on the Se substitution in Ni1-xS or NiS1-y Sey ( dE B/ dxapprox 0; dE B/ dyapprox 0). The Ni 2p3/2 core level peak also shifts toward lower E B ( dE B/ dv=-1.8± 0.6 eV/mol), while no change in the S 2s or 2p core level peak is observed. We propose the possibility that the hybridization between the Co d7L and the Ni d8L peaks near the E F, where L denotes a ligand hole, leads to the modification of the electronic state of Ni sites in Ni1-vCovS.

Thermal Expansion Behaviours through the Charge-Transfer Type Nonmetal-Metal Transition in Ni_1-rM_rS (M=Ti, V and Cr)

Masanori Matoba, Shuichiro Anzai and Mitsuya Uchida

Journal of the Physical Society of Japan 61 1425-1426 1992

Research paper (scientific journal), Joint Work, Lead author, Accepted

Thermal Expansion, Thermoelectric Power, and XPS Study of the Nonmeta-Metal Transition in Ni_1-xS_1-ySe_y

Masanori Matoba, Shuichiro Anzai and Atsushi Fujimori

Journal of the Physical Society of Japan 60 4230-4244 1991

Research paper (scientific journal), Joint Work, Lead author, Accepted

Magnetic susceptibility χ, electrical resistivity ρ, thermoelectric power S, XPS spectra and hexagonal lattice parameters c and a are measured on the NiAs-type Ni_1-x_S_1-y_Se_y_ (x≤0.04; y≤1.00). We find the followings (1) the nonmetal-metal transition temperature T_t_, the phonon-drag coefficient C below T_t_ and dχ(T>T_t_)/dT decrease and they are suppressed at x_c_ and y_c_ with increase in x and y, respectively. (2) The nearest neighboring S_1-y_Se_y_(Z)-Z, Ni-Z and Ni-Ni distances just below T_t_ (D_Z-Z_N, D_Ni-Z_N, D_Ni-Ni_N, respectively) are depressed with increase in x. D_Z-Z_N and D_Ni-Ni_N only slightly depend on y, while D_Ni-Z_N increases with increasing y. (3) No change in the d8L peak (L: hole in the Z network) in the valence band region is observed among Ni_1-x_S_1-y_Se_y_ and Ni_0.93_Te. (4) The Ni 2p_3/2_d^9^L core level peak shifts to lower binding energy E_B_ with increasing y, while it hardly changes with x. (5) The E_B_ of S 2s and S 2p core levels decrease with increasing textotx; the EB of S 2p one decreases with increasing y. From the view point of the charge-transfer model, the pressure and the Ni-vacancy substitution effects on Tt are mainly explained by the increase in the Z(p) band width, and the Se-substitution effect by the decrease in the charge-transfer energy. The Ni-vacancies also introduce extra holes in the Z(p) band.

Photoemission study of the metal-nonmetal transition in NiS

Atsushi Fujimori, Hirofumi Namatame, Masanori Matoba and Shuichiro Anzai

Physical Review B 42 620-623 1990.07

Research paper (scientific journal), Joint Work, Accepted

We have observed small changes in the ultraviolet photoemission spectra of NiS across the temperature-induced phase transition between the Pauli-paramagnetic metal and the antiferromagnetic nonmetal. In going from the nonmetallic to the metallic phases, the main band (d8L) within ~3 eV below the Fermi level EF is shifted toward EF by 0.05 eV. This observation is consistent with the closing of a S 3p–Ni 3d charge-transfer gap and cannot be reconciled with that of a band gap of antiferromagnetic origin. The spectrum loses a small fraction of intensity in the vicinity of EF as the gap is collapsed. The virtually identical line shape of the main band between the two phases is consistent with the persistence of short-range antiferromagnetic correlation in the paramagnetic phase.

Conductivity Phase Transition with Shift of Valence-Band Edge and with Structural Distortion in Cu₄Sn_1-xGe_xS₄

Takayuki Kamimura, Masanori Matoba and Shuichiro Anzai

Journal of the Physical Society of Japan 59 3045-3048 1990.06

Research paper (scientific journal), Joint Work, Accepted

X-ray diffraction, electrical resistivity, DSC and XPS investigations were carried out on Cu4Sn1-xGexS4 (0≤x≤1.0). At room temperature, the orthorhombic structure changes to a monoclinic one at a transition concentration of xt=0.6 as x increases. This transition also exhibits the expansions in the energy width between the top of the valence band and the Fermi level and in the lattice parameter B. The transition has the characteristics of the first-order high (high temperature)-to-low (low temperature) conductivity phase transition as reported on Cu4SnS4. The transition temperature Tt linearly increases with x. These features are briefly compared with the electronic and structural phase transition reported on SnTe and Pb1-xGexTe.

高電導性半導体Cu₄SnS₄の電導度相転移に対する不純物置換の物性制御効果

安西修一郎, 井上郁也, 的場正憲, 上村隆之

旭硝子財団研究報告 57 229-239 1990

Research paper (other academic), Joint Work

Conductivity Phase Transition in Cu₄Sn(S_1-ySe_y)₄

Shuichiro Anzai, Masanori Matoba, Ikuya Inoue, Tadahiro Fukazawa, Takayuki Kamimura and Kazuhiko Kitamura

Journal of the Physical Society of Japan 59 3799-3800 1990

Research paper (scientific journal), Joint Work, Accepted

Cu₄SnS₄の熱電能

的場正憲, 井上郁也, 上村隆之, 渡辺守生, 安西修一郎

日本材料科学会誌 27 299-301 1990

Research paper (scientific journal), Joint Work, Lead author, Accepted

Electron correlation and magnetism in NiS: Implications of photoemission spectra

Atsushi Fujimori, Kiyoyuki Terakura, Masaki Taniguchi, Susumu Ogawa, Shigemasa Suga, Masanori Matoba and Shuichiro Anzai

Physical Review B 37 3109-3112 1988.02

Research paper (scientific journal), Joint Work, Accepted

熱電能(室温以下)の測定法と高温超伝導体YBa₂Cu₃O_7-xへの応用

的場正憲, 安西修一郎, 王子雅章

日本材料科学会誌 25 173-176 1988

Research paper (scientific journal), Joint Work, Lead author, Accepted

Electron correlation and magnetism in NiS: Implications of photoemission spectra

Atsushi Fujimori, Kiyoyuki Terakura, Masaki Taniguchi, Susumu Ogawa, Shigemasa Suga, Masanori Matoba and Shuichiro Anzai

Technical Report of the Institute for Solid State Physics 1987 1-14 1987

Research paper (other academic), Joint Work

The T²-Contribution to the Electrical Resistivity at Low Temperatures in NiAs-type Ni_1-xS_1-ySe_y

Masanori Matoba and Shuichiro Anzai

Journal of Magnetism and Magnetic Materials 70 213-214 1987

Research paper (scientific journal), Joint Work, Lead author, Accepted

Localized versus Itinerant Character of d Electrons in NiS: Photoemission Spectroscopic Study

Atsushi Fujimori, Masanori Matoba, Shuichiro Anzai, Kiyoyuki Terakura, Masaki Taniguchi, Susumu Ogawa and Shigemasa Suga

Journal of Magnetism and Magnetic Materials 70 67-69 1987

Research paper (scientific journal), Joint Work, Accepted

Photoemission Study of the Electronic Structure and the Metal-nonmetal Transition in NiS

Atsushi Fujimori, Masanori Matoba, Shuichiro Anzai, Masaki Taniguchi, Susumu Ogawa, and Shigemasa Suga

Activity Report of Synchrotron Radiation Laboratory 1986 51-52 1986

Research paper (other academic), Joint Work

Effect of Se-Substitution on the Magnetic and Electrical Transition in the NiAs-type NiS

Shuichiro Anzai, Masanori Matoba, Masakazu Hatori and Hiroshi Sakamoto

Journal of the Physical Society of Japan 55 2531-2534 1986

Research paper (scientific journal), Joint Work, Accepted

Hexagonal lattice parameters a and c of the NiAs-type NiS_1-y_Se_y_ expand with increasing y below the solubility limit y_L_=0.20. The first-order transition temperature T_t_(y) [between the antiferromagnetic less-conductive and the Pauli-paramagnetichigh-conductive states] decreases with increasing y, and is suppressed down to 4.2K at the critical concentration y_c_=0.l33. Just above T_t_, the temperature slope of the susceptibility has positive sign at low y, and shows a y-dependence. The isothermal susceptibility of the Pauli-paramagnetic state decreases with increasing y. These experimental results are discussed on the basis of the strongly correlated features of d and p bands in NiS.

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