2024/12/09 更新

写真b

フジワラ コウヘイ
藤原 宏平
FUJIWARA KOHEI
*大学が定期的に情報更新している項目(その他は、researchmapの登録情報を転載)
所属*
理学部 化学科
理学研究科 化学専攻 博士課程後期課程
理学研究科 化学専攻 博士課程前期課程
職名*
准教授
学位
博士(科学) ( 東京大学 )
研究テーマ*
  • 薄膜物性化学、機能物質化学。真空成膜技術を駆使して、機能物性の発現が期待される無機固体物質を薄膜化する。バルク不安定な相の安定化による新物質創製や積層構造における界面物性制御などを通して、無機固体の物性を人工的に拡張・増強するための学理を構築するとともに、見出した物質や機能を各種材料やデバイス原理へと応用することにも取り組んでいる。

  • 研究キーワード
  • 薄膜・界面物性

  • 無機固体化学

  • 機能性酸化物

  • トポロジカル物質

  • 酸化物エレクトロニクス

  • スピントロニクス

  • 学内職務経歴*
    • 2024年4月 - 現在 
      理学部   化学科   准教授
    • 2024年4月 - 現在 
      理学研究科   化学専攻 博士課程前期課程   准教授
    • 2024年4月 - 現在 
      理学研究科   化学専攻 博士課程後期課程   准教授
     

    経歴

    • 2024年4月 - 現在 
      立教大学   理学部化学科   准教授

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    • 2023年4月 - 現在 
      科学技術振興機構   創発研究者

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    • 2018年10月 - 2024年3月 
      東北大学   金属材料研究所   准教授

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    • 2015年4月 - 2018年9月 
      東北大学   金属材料研究所   講師

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    • 2011年2月 - 2015年3月 
      大阪大学   産業科学研究所 産業科学ナノテクノロジーセンター   助教

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    • 2008年4月 - 2011年1月 
      理化学研究所   高木磁性研究室   基礎科学特別研究員

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    学歴

    • - 2008年3月 
      東京大学   新領域創成科学研究科   物質系専攻

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      国名: 日本国

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    • - 2005年3月 
      東京大学   新領域創成科学研究科   物質系専攻

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      国名: 日本国

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    • - 2003年3月 
      東京大学   理学部   化学科

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      国名: 日本国

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    委員歴

    • 2024年9月 - 現在 
      Communications Materials   Editorial Board Member

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      団体区分:その他

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    • 2023年4月 - 2026年3月 
      電気学会電子材料技術委員会   1号委員

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      団体区分:学協会

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    • 2021年4月 - 2026年3月 
      日本学術振興会産学協力委員会R031ハイブリッド量子ナノ技術委員会   委員

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      団体区分:学協会

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    • 2023年6月 - 2025年3月 
      電気学会エコシステム材料技術調査専門委員会   幹事

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    • 2020年11月 - 2025年3月 
      日本学術振興会産学協力委員会R025先進薄膜界面機能創成委員会   委員

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      団体区分:学協会

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    • 2019年6月 - 2024年3月 
      Scientific Reports   Editorial Board Member

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      団体区分:その他

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    • 2023年3月 - 2023年3月 
      令和5年電気学会全国大会シンポジウム S9「Society5.0 に向けた革新的材料・プロセス・デバ イス開発の最前線」   世話人代表

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      団体区分:学協会

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    • 2021年4月 - 2023年3月 
      電気学会エマージングフレキシブルデバイス材料技術調査専門委員会   委員長

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      団体区分:学協会

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    • 2022年9月 - 2022年9月 
      International Symposium on Control of Semiconductor Interfaces (ISCSI-IX)   運営委員

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      団体区分:学協会

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    • 2021年12月 - 2021年12月 
      Materials Research Meeting 2021, Symposium D-2: Frontier in Functional Oxides and Related Materials: from Materials Design to Device Applications   運営委員

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      団体区分:学協会

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    • 2021年9月 - 2021年9月 
      応用物理学会第82回秋季学術講演会シンポジウムT9「固相における秩序とは何か︓機能を⽣み出す秩序の概念展開」   世話人

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      団体区分:学協会

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    • 2020年12月 - 2020年12月 
      第30回日本MRS年次大会シンポジウムB: 先進機能性酸化物材料-作製プロセスおよび物性評価-   運営委員

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      団体区分:学協会

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    • 2018年8月 - 2020年7月 
      電気学会フレキシブルセラミックスコーティング技術調査専門委員会   委員

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      団体区分:学協会

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    • 2012年8月 - 2020年3月 
      文部科学省科学技術政策研究所科学技術動向研究センター   専門調査員

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    • 2019年12月 - 2019年12月 
      日本MRS   Materials Research Meeting 2019, Symposium H-3: Advanced Functional Oxides: Processing, Characterization, and Devices, 運営委員

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      団体区分:学協会

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    • 2017年11月 - 2018年11月 
      電気学会電子材料研究会「フレキシブルセラミックスコーティング研究会」   運営委員

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      団体区分:学協会

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    • 2018年10月 - 2018年10月 
      4th E-MRS & MRS-J Bilateral Symposium, Symposium 2: Processing and characterization of advanced multifunctional oxides   運営委員

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      団体区分:学協会

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    • 2016年5月 - 2018年4月 
      電気学会フレキシブルコーティング技術調査専門委員会   委員

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      団体区分:学協会

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    • 2018年3月 - 2018年3月 
      応用物理学会第65回春季学術講演会シンポジウムS7「フレキシブルセラミックスコーティング技術と有機・無機ハイブリッドフレキシブルデバイスの新展開」   世話人

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      団体区分:学協会

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    • 2017年8月 - 2017年8月 
      International Union of Materials Research Societies – International Conference on Advanced Materials 2017, Symposium A-4: Magnetic oxide thin films and hetero-structures   運営委員

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      団体区分:学協会

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    • 2014年6月 - 2014年6月 
      International Union of Materials Research Societies – International Conference on Electronic Materials 2014, Symposium F: Oxide materials for advanced electronics   運営委員

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      団体区分:学協会

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    受賞

    • 2024年9月  
      電気学会  2023年度電子・情報・システム部門査読促進賞 

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    • 2024年5月  
      東北大学金属材料研究所新素材共同研究開発センター  第18回共同利用研究課題最優秀賞 

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    • 2019年11月  
      日本MRS  日本MRS貢献賞 

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      受賞区分:国内学会・会議・シンポジウム等の賞 

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    • 2015年1月  
      日本MRS  日本MRS奨励賞 

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      受賞区分:国内学会・会議・シンポジウム等の賞 

      受賞国:日本国

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    • 2014年9月  
      日本MRS  Award for Encouragement of Research in IUMRS-ICA 2014 (2) 

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    • 2014年9月  
      日本MRS  Award for Encouragement of Research in IUMRS-ICA 2014 (1) 

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      受賞区分:国内学会・会議・シンポジウム等の賞 

      受賞国:日本国

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    • 2013年12月  
      Materials Research Society  2013 Materials Research Society Fall Meeting, Best Poster Award 

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      受賞区分:国内学会・会議・シンポジウム等の賞 

      受賞国:日本国

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    • 2013年10月  
      応用物理学会関西支部  平成25年度第2回講演会ポスター賞(優秀賞) 

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      受賞区分:国内学会・会議・シンポジウム等の賞 

      受賞国:日本国

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    • 2013年9月  
      応用物理学会  第34回応用物理学会講演奨励賞 

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      受賞区分:国内学会・会議・シンポジウム等の賞 

      受賞国:日本国

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    • 2010年9月  
      応用物理学会  第32回応用物理学会論文奨励賞 

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      受賞区分:国内学会・会議・シンポジウム等の賞 

      受賞国:日本国

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    論文

    • Giant antisymmetric magnetoresistance arising across optically controlled domain walls in the magnetic Weyl semimetal Co3Sn2S2 査読有り

      Kohei Fujiwara, Kazuma Ogawa, Naotaka Yoshikawa, Koji Kobayashi, Kentaro Nomura, Ryo Shimano, Atsushi Tsukazaki

      Communications Materials5   239   2024年11月

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      担当区分:筆頭著者, 責任著者   記述言語:日本語  

      DOI: 10.1038/s43246-024-00688-w

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    • Suppression of cracking induced by epitaxial strain relaxation using a relaxation absorber during the transfer of epitaxial thin films of anatase-type Nb:TiO2 査読有り

      Hiroaki Nishikawa, Akihiro Hiraoka, Kaori Sato, Shun Ito, Nobuhiro Kato, Kohei Fujiwara

      Thin Solid Films807   140531 - 140531   2024年10月

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      掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

      DOI: 10.1016/j.tsf.2024.140531

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    • Strongly pinned skyrmionic bubbles and higher-order nonlinear Hall resistances at the interface of Pt/FeSi bilayer 査読有り

      T. Hori, N. Kanazawa, K. Matsuura, H. Ishizuka, K. Fujiwara, A. Tsukazaki, M. Ichikawa, M. Kawasaki, F. Kagawa, M. Hirayama, Y. Tokura

      Physical Review Materials8 ( 4 ) 044407   2024年4月23日

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      掲載種別:研究論文(学術雑誌)   出版者・発行元:American Physical Society (APS)  

      DOI: 10.1103/physrevmaterials.8.044407

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      その他リンク: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevMaterials.8.044407/fulltext

    • Bipolarity of large anomalous Nernst effect in Weyl magnet-based alloy films 査読有り

      Shun Noguchi, Kohei Fujiwara, Yuki Yanagi, Michi-To Suzuki, Takamasa Hirai, Takeshi Seki, Ken-ichi Uchida, Atsushi Tsukazaki

      Nature Physics20   254 - 260   2024年1月

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      担当区分:責任著者  

      DOI: 10.1038/s41567-023-02293-z

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    • Intercorrelated anomalous Hall and spin Hall effect in kagome-lattice Co3Sn2S2-based shandite films 査読有り

      Yong-Chang Lau, Junya Ikeda, Kohei Fujiwara, Akihiro Ozawa, Jiaxin Zheng, Takeshi Seki, Kentaro Nomura, Liang Du, Quansheng Wu, Atsushi Tsukazaki, Koki Takanashi

      Physical Review B108 ( 6 )   2023年8月25日

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      掲載種別:研究論文(学術雑誌)   出版者・発行元:American Physical Society (APS)  

      DOI: 10.1103/physrevb.108.064429

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      その他リンク: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.108.064429/fulltext

    • Berry curvature contributions of kagome-lattice fragments in amorphous Fe–Sn thin films 査読有り

      Kohei Fujiwara, Yasuyuki Kato, Hitoshi Abe, Shun Noguchi, Junichi Shiogai, Yasuhiro Niwa, Hiroshi Kumigashira, Yukitoshi Motome, Atsushi Tsukazaki

      Nature Communications14 ( 1 ) 3399   2023年6月

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      担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)  

      DOI: 10.1038/s41467-023-39112-1

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      その他リンク: https://www.nature.com/articles/s41467-023-39112-1

    • Improvement of superconducting properties in La1-xSrxNiO2 thin films by tuning topochemical reduction temperature 査読有り

      Motoki Osada, Kohei Fujiwara, Tsutomu Nojima, Atsushi Tsukazaki

      Physical Review Materials7 ( 5 )   2023年5月18日

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      掲載種別:研究論文(学術雑誌)   出版者・発行元:American Physical Society (APS)  

      DOI: 10.1103/physrevmaterials.7.l051801

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      その他リンク: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevMaterials.7.L051801/fulltext

    • Thin-film magnetic sensors using topological materials 招待有り

      Kohei Fujiwara, Junichi Shiogai, Atsushi Tsukazaki

      JSAP Review2023   230414   2023年5月

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      担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)  

      DOI: 10.11470/jsaprev.230414

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    • Enhancement of spin-charge conversion efficiency for Co3Sn2S2 across transition from paramagnetic to ferromagnetic phase 査読有り

      Takeshi Seki, Yong-Chang Lau, Junya Ikeda, Kohei Fujiwara, Akihiro Ozawa, Satoshi Iihama, Kentaro Nomura, Atsushi Tsukazaki

      Physical Review Research5 ( 1 )   2023年3月31日

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      掲載種別:研究論文(学術雑誌)   出版者・発行元:American Physical Society (APS)  

      DOI: 10.1103/physrevresearch.5.013222

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      その他リンク: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevResearch.5.013222/fulltext

    • Electrochemical thinning of Co kagome-lattice layers in ferromagnetic Co3Sn2S2 thin films by bias-induced Co dissolution 査読有り

      K. Fujiwara, J. Ikeda, S. Ito, A. Tsukazaki

      Journal of Applied Physics133   125302   2023年3月

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      担当区分:筆頭著者, 責任著者   記述言語:英語  

      DOI: 10.1063/5.0134291

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    • Composition tuning of Mg/Ir ratio and crystallization of a spinel-related structure in Mg-Ir-O films by pulsed-laser deposition 査読有り

      Masamichi Negishi, Kohei Fujiwara, Atsushi Tsukazaki

      Thin Solid Films769   139740 - 139740   2023年3月

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      掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

      DOI: 10.1016/j.tsf.2023.139740

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    • Non-volatile chirality switching by all-optical magnetization reversal in ferromagnetic Weyl semimetal Co3Sn2S2 査読有り

      Naotaka Yoshikawa, Kazuma Ogawa, Yoshua Hirai, Kohei Fujiwara, Junya Ikeda, Atsushi Tsukazaki, Ryo Shimano

      Communications Physics5 ( 1 ) 32   2022年12月20日

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      掲載種別:研究論文(学術雑誌)   出版者・発行元:Springer Science and Business Media LLC  

      Abstract

      Weyl semimetals show unique physical properties exemplified by the colossal anomalous Hall effect, arising from exotic quasiparticles called Weyl fermions emerging around the Weyl nodes. Manipulating these topologically protected Weyl nodes is anticipated to play a leading role towards the on-demand control of quantum properties in Weyl semimetals. We demonstrate non-volatile chirality switching in a ferromagnetic Weyl semimetal Co<sub>3</sub>Sn<sub>2</sub>S<sub>2</sub> via all-optical magnetization reversal. When excited by circularly polarized mid-infrared light pulses, the sign reversal of the anomalous Hall conductivity stemming from the Berry curvature is observed, manifesting the switching of the chirality of the Weyl nodes accompanying with the magnetization reversal. Magneto-optical imaging measurements reveal that the mechanism of the magnetization/chirality switching is attributed to the helicity-dependent deterministic magnetization associated with the magnetic circular dichroism.

      DOI: 10.1038/s42005-022-01106-8

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      その他リンク: https://www.nature.com/articles/s42005-022-01106-8

    • Electrical detection of domain evolution in magnetic Weyl semimetal Co3Sn2S2 submicrometer-wide wire devices 査読有り

      Junichi Shiogai, Junya Ikeda, Kohei Fujiwara, Takeshi Seki, Koki Takanashi, Atsushi Tsukazaki

      Physical Review Materials6 ( 11 )   2022年11月30日

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      掲載種別:研究論文(学術雑誌)   出版者・発行元:American Physical Society (APS)  

      DOI: 10.1103/physrevmaterials.6.114203

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      その他リンク: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevMaterials.6.114203/fulltext

    • Noble‐Metal Free Spintronic System with Proximity‐Enhanced Ferromagnetic Topological Surface State of FeSi Above Room Temperature 査読有り

      Tomohiro Hori, Naoya Kanazawa, Motoaki Hirayama, Kohei Fujiwara, Atsushi Tsukazaki, Masakazu Ichikawa, Masashi Kawasaki, Yoshinori Tokura

      Advanced Materials   2206801 - 2206801   2022年11月4日

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      掲載種別:研究論文(学術雑誌)   出版者・発行元:Wiley  

      DOI: 10.1002/adma.202206801

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    • A large unidirectional magnetoresistance in Fe-Sn heterostructure devices 査読有り

      Junichi SHIOGAI, Kohei Fujiwara, Tsutomu Nojima, Atsushi TSUKAZAKI

      Japanese Journal of Applied Physics   2022年6月23日

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      掲載種別:研究論文(学術雑誌)   出版者・発行元:IOP Publishing  

      Abstract

      Unidirectional magnetoresistance (UMR) is an attractive magnetic-field sensing technique as it enables detecting the in-plane direction of the external magnetic field with a single element. However, the UMR amplitude is typically several orders of magnitude smaller than those of other directional magnetoresistances exhibited in ferromagnetic thin films, hindering sensing applications using the UMR. For a directional magnetic sensor using the UMR, the in-depth understanding of mechanisms of the UMR and its enhancement are highly desirable. In this study, the structural dependence of the UMR in Fe-Sn heterostructure devices is investigated. We find a weak dependence of the UMR on interface configuration in the oxide cap/Fe-Sn heterostructures on various oxide substrates. In contrast, the normalized UMR amplitude is enhanced by a factor of 27 with increasing the Fe-Sn layer thickness from 4.0 to 100 nm. These results suggest that the magnetothermal effect dominates the large UMR in the Fe-Sn heterostructure devices.

      DOI: 10.35848/1347-4065/ac7bc8

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      その他リンク: https://iopscience.iop.org/article/10.35848/1347-4065/ac7bc8/pdf

    • L21 ordering of Co2FeSn thin films promoted by high-temperature annealing 査読有り

      Kohei Fujiwara, Koya Shibata, Shunsuke Nishimura, Junichi Shiogai, Atsushi Tsukazaki

      AIP Advances12 ( 6 ) 065030 - 065030   2022年6月1日

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      担当区分:筆頭著者, 責任著者   掲載種別:研究論文(学術雑誌)   出版者・発行元:AIP Publishing  

      We report the effect of annealing on the crystalline ordering and physical properties in thin films of a nodal line semimetal candidate L2<sub>1</sub>-type Co<sub>2</sub>FeSn. The Co–Fe–Sn films with a composition of Co:Fe:Sn ∼ 2:1:1 were deposited on MgO(001) substrates at a substrate temperature of 150 °C by radio-frequency magnetron sputtering. The as-deposited film showed x-ray diffraction patterns corresponding to the B2 ordering. Annealing at 600 and 700 °C after the deposition resulted in the appearance of the (111) diffraction peak, which is characteristic of the L2<sub>1</sub> ordering. Although anomalous Hall conductivity and transverse thermoelectric conductivity decreased from those of the as-deposited film with the annealing-induced L2<sub>1</sub> ordering, the low anomalous Hall conductivity of the 700 °C-annealed film was consistent with the theoretically estimated low value. These results show the significant influence of crystalline ordering on the electrical and thermoelectric transport properties. The annealing process is beneficial for studying the exotic physics arising from topological band features in the L2<sub>1</sub>-ordered Co<sub>2</sub>FeSn thin films.

      DOI: 10.1063/5.0093195

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    • Formation of ilmenite-type single-crystalline MgTiO3 thin films by pulsed-laser deposition 査読有り

      Masamichi Negishi, Kohei Fujiwara, Atsushi Tsukazaki

      AIP Advances11 ( 12 ) 125125 - 125125   2021年12月27日

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      掲載種別:研究論文(学術雑誌)   出版者・発行元:AIP Publishing  

      DOI: 10.1063/5.0078021

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    • Improvement of the detectivity in an Fe-Sn magnetic-field sensor with a large current injection 査読有り

      Junichi SHIOGAI, Zhenhu Jin, Yosuke Satake, Kohei Fujiwara, Atsushi TSUKAZAKI

      Japanese Journal of Applied Physics   2021年12月24日

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      掲載種別:研究論文(学術雑誌)   出版者・発行元:IOP Publishing  

      Abstract

      A ferromagnetic nanocrystalline Fe-Sn is an excellent platform for magnetic-field sensor based on anomalous Hall effect (AHE) owing to simple fabrication and superior thermal stability. For improvement of the magnetic-field sensitivity, doping impurity and increasing injection current are effective approaches. However, in the light of magnetic-field detectivity, the large current may increase the voltage noise. In this study, a maximum allowable current of was improved by employing the overlayer electrode configuration on a Ta-doped Fe-Sn AHE sensor. In noise measurements, the 1/f noise becomes significant with increasing the current at low frequency, resulting in saturation of the detectivity to 240 nTHz-1/2 at 120 Hz. At high frequency, the detectivity reaches 48 nTHz-1/2 at 3.1 mA showing ten times improvement of the detectivity compared with the non-doped Fe-Sn AHE sensor. Material design and device structure optimization will accelerate further improvement of the sensing properties of the Fe-Sn-based AHE sensor.

      DOI: 10.35848/1347-4065/ac465a

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      その他リンク: https://iopscience.iop.org/article/10.35848/1347-4065/ac465a/pdf

    • Emergence of spin-orbit coupled ferromagnetic surface state derived from Zak phase in a nonmagnetic insulator FeSi 査読有り

      Yusuke Ohtsuka, Naoya Kanazawa, Motoaki Hirayama, Akira Matsui, Takuya Nomoto, Ryotaro Arita, Taro Nakajima, Takayasu Hanashima, Victor Ukleev, Hiroyuki Aoki, Masataka Mogi, Kohei Fujiwara, Atsushi Tsukazaki, Masakazu Ichikawa, Masashi Kawasaki, Yoshinori Tokura

      Science Advances7 ( 47 ) eabj0498   2021年11月19日

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      掲載種別:研究論文(学術雑誌)   出版者・発行元:American Association for the Advancement of Science (AAAS)  

      Ferromagnetic-metal surface state derived from topological polarization and its spin-orbitronics functionalities in FeSi.

      DOI: 10.1126/sciadv.abj0498

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    • Tuning scalar spin chirality in ultrathin films of the kagome-lattice ferromagnet Fe3Sn 査読有り 国際誌

      K. Fujiwara, Y. Kato, T. Seki, K. Nomura, K. Takanashi, Y. Motome, A. Tsukazaki

      Communications Materials2 ( 1 ) 113   2021年11月

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      担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)  

      DOI: 10.1038/s43246-021-00218-y

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      その他リンク: https://www.nature.com/articles/s43246-021-00218-y

    • Three-dimensional sensing of the magnetic-field vector by a compact planar-type Hall device 査読有り

      Junichi Shiogai, Kohei Fujiwara, Tsutomu Nojima, Atsushi Tsukazaki

      Communications Materials2 ( 1 ) 102   2021年10月

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

      Smart society is forthcoming with a rapid development in the automation of electric appliances requiring abundant sensors. One of the key sensors is a three-dimensional magnetometer for detecting the motion of objects, which is usually driven by cooperative multiple sensors on three orthogonal planes. Here, we demonstrate the fundamental operation of a three-dimensional magnetometer based on a simple Fe-Sn heterostructure Hall device in a planar geometry. Polar coordinates of the magnetic-field vector are uniquely determined by the combination of the sizable anomalous Hall effect, the anisotropic magnetoresistance, and the unidirectional magnetoresistance. Thanks to the ferromagnetic topological features in the Fe-Sn heterostructure, the above-mentioned device overcomes the limitation of conventional semiconductor devices and is highly sensitive even at room temperature. The compact planar geometry will be particularly useful in versatile electrical applications requiring a low-cost three-dimensional magnetometer with space- and energy-saving features.Three-dimensional magnetometers are key for detecting the motion of objects in automated electronics, but typically require multiple sensors on orthogonal planes. Here, a compact planar-type 3D magnetometer with low power consumption is realized using a topological ferromagnetic Fe-Sn heterostructure.

      DOI: 10.1038/s43246-021-00206-2

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    • Electrostatic carrier doping of charge-ordered YbFe2O4 thin films using ionic liquids 査読有り

      Kohei Fujiwara, Tatsuya Hori, Hidekazu Tanaka

      Applied Physics Express14 ( 8 ) 083001 - 083001   2021年7月15日

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      担当区分:筆頭著者, 責任著者   掲載種別:研究論文(学術雑誌)   出版者・発行元:IOP Publishing  

      DOI: 10.35848/1882-0786/ac114e

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      その他リンク: https://iopscience.iop.org/article/10.35848/1882-0786/ac114e/pdf

    • 水溶性Sr3Al2O6犠牲層を用いたアナターゼ型Nb:TiO2エピタキシャル薄膜のフレキシブル化プロセス 査読有り

      平岡壮大, 藤原宏平, 西川博昭

      電気学会論文誌C141 ( 7 ) 767 - 770   2021年7月1日

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      掲載種別:研究論文(学術雑誌)  

      DOI: 10.1541/ieejeiss.141.767

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    • Two-dimensionality of metallic surface conduction in Co3Sn2S2 thin films 査読有り

      Junya Ikeda, Kohei Fujiwara, Junichi Shiogai, Takeshi Seki, Kentaro Nomura, Koki Takanashi, Atsushi Tsukazaki

      Communications Physics4 ( 1 ) 117   2021年6月

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      担当区分:責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Springer Science and Business Media LLC  

      <title>Abstract</title>Two-dimensional (2D) surface of the topological materials is an attractive channel for the electrical conduction reflecting the linearly-dispersive electronic bands. Thickness-dependent sheet conductance measurement is a reliable method to evaluate the 2D and three-dimensional (3D) electrical conducting channel separately but has rarely been applied for Weyl semimetals. By applying this method to thin films of a Weyl semimetal Co<sub>3</sub>Sn<sub>2</sub>S<sub>2</sub>, here we show that the 2D conducting channel clearly emerges under the ferromagnetic phase, indicating a formation of the Fermi arcs projected from Weyl nodes. Comparison between 3D conductivity and 2D conductance provides the effective thickness of the surface conducting region being estimated to be approximately 20 nm, which would reflect the Weyl feature of electronic bands of the Co<sub>3</sub>Sn<sub>2</sub>S<sub>2</sub>. The emergent surface conduction will provide a pathway to activate quantum and spintronic transport features stemming from a Weyl node in thin-film-based devices.

      DOI: 10.1038/s42005-021-00627-y

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      その他リンク: http://www.nature.com/articles/s42005-021-00627-y

    • First-principles investigation of magnetic and transport properties in hole-doped shandite compounds Co3InxSn2−xS2 査読有り

      Yuki Yanagi, Junya Ikeda, Kohei Fujiwara, Kentaro Nomura, Atsushi Tsukazaki, Michi-To Suzuki

      Physical Review B103 ( 20 ) 205112   2021年5月7日

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      記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Physical Society (APS)  

      Co-based shandite Co3Sn2S2 is a representative example of magnetic Weyl semimetals showing rich transport phenomena. We thoroughly investigatemagnetic and transport properties of hole-doped shandites Co3InxSn2-xS2 by first-principles calculations. The calculations reproduce nonlinear reduction of anomalous Hall conductivity with doping In for Co3Sn2S2 as reported in experiments against the linearly decreased ferromagnetic moment within virtual crystal approximation. We show that a drastic change in the band parity character of Fermi surfaces, attributed to the nodal rings lifted energetically with In doping, leads to strong enhancement of anomalous Nernst conductivity with reversing its sign in Co3InxSn2-xS2.

      DOI: 10.1103/physrevb.103.205112

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      その他リンク: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.103.205112/fulltext

    • Critical thickness for the emergence of Weyl features in Co3Sn2S2 thin films 査読有り

      J. Ikeda, K. Fujiwara, J. Shiogai, T. Seki, K. Nomura, K. Takanashi, A. Tsukazaki

      Communications Materials2 ( 1 ) 18   2021年2月18日

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      担当区分:責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:SPRINGERNATURE  

      Magnetic Weyl semimetals are quantum phases of matter arising from the interplay of linearly dispersive bands, spin-orbit coupling, and time reversal symmetry breaking. This can be realised, for example, in Co3Sn2S2, based on a cobalt kagome lattice and characterised by intriguing phenomena such as large anomalous Hall effect, Nernst effect, and water oxidation. Here, we attempt to determine the robustness of the twofold necessary conditions for the emergence of the magnetic Weyl semimetal phase in Co3Sn2S2 ultrathin films. Except for two-dimensional layered materials, a reduction of thickness generally makes it difficult to develop topological character and ferromagnetic long-range order. In Co3Sn2S2 films, while ferromagnetic ordering appears robustly even in average thicknesses of one or two unit cells with island-like polycrystalline domains, the anomalous Hall conductivity appears only above a critical thickness of approximately 10 nm. The emergence of surface conduction and large anomalous Hall effect implies the distinct contribution of Weyl nodes and their Berry curvature. These findings reveal an exotic feature of Weyl physics in thin-film based superstructures as well as a potential for future applications in electronic devices.The coexistence of ferromagnetism and topology has recently attracted intense interest. Here, the thickness dependence of magnetisation and anomalous Hall conductivity is investigated in Co3Sn2S2 thin films, revealing a critical thickness of 10 nm for the emergence of the magnetic Weyl semimetal phase.

      DOI: 10.1038/s43246-021-00122-5

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    • Robust perpendicular magnetic anisotropy of Co3Sn2S2 phase in sulfur deficient sputtered thin films 査読有り

      Junichi Shiogai, Junya Ikeda, Kohei Fujiwara, Takeshi Seki, Koki Takanashi, Atsushi Tsukazaki

      Physical Review Materials5 ( 2 )   2021年2月9日

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      記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Physical Society (APS)  

      Perpendicular magnetic anisotropy (PMA) in magnetic thin films is a fundamental key feature in the design of spintronic devices. As one of magnetic Weyl semimetals, Co3Sn2S2 has been studied for its large anomalous Hall effect (AHE), uniaxial crystalline magnetic anisotropy, and half metallicity. In this study, we investigated the effect of off-stoichiometric composition on the PMA and AHE of Co3Sn2S2, thin films fabricated by the sputtering technique. The prepared thin films have off-stoichiometric S compositions x of 1.54 (S poor) and 3.27 (S rich) as well as the nearly stoichiometric one of 2.02. In addition to the Co3Sn2S2 phase, the segregated Co metal is found to contribute to the measured magnetization in the S-poor and S-rich films. The coercive field of perpendicular magnetization in all the films is much larger than that in the Co3Sn2S2 bulk crystals despite the fact that effective perpendicular magnetic anisotropy constants (K-u(eff)) between the prepared films are significantly different. In addition, the K-u(eff) values of two samples with x = 2.02 and 2.22 are comparable to those of the bulk crystals. In contrast to the isotropic magnetization behavior in the S-rich film, the S-poor film holds the PMA feature. This result means that the PMA is more robust in the S-poor film than in the S-rich film. For the electrical transport properties, a large tangent of Hall angle of about 0.2 is observed for both the nearly stoichiometric and the S-poor films. This large tangent of Hall angle demonstrates that the Weyl feature of Co3Sn2S2 phase is well maintained even in the S-poor thin films as well as the nearly stoichiometric films although the amount of Co segregation in both S-poor and S-rich films is similar. Our findings on the influence of off-stoichiometry on the PMA and AHE are beneficial to design magnetic devices incorporated with the Weyl features of Co3Sn2S2.

      DOI: 10.1103/physrevmaterials.5.024403

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      その他リンク: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevMaterials.5.024403/fulltext

    • Giant magneto-optical responses in magnetic Weyl semimetal Co3Sn2S2 査読有り

      Y. Okamura, S. Minami, Y. Kato, Y. Fujishiro, Y. Kaneko, J. Ikeda, J. Muramoto, R. Kaneko, K. Ueda, V. Kocsis, N. Kanazawa, Y. Taguchi, T. Koretsune, K. Fujiwara, A. Tsukazaki, R. Arita, Y. Tokura, Y. Takahashi

      Nature Communications11 ( 1 ) 4629   2020年12月

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      記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Springer Science and Business Media LLC  

      <title>Abstract</title>
      The Weyl semimetal (WSM), which hosts pairs of Weyl points and accompanying Berry curvature in momentum space near Fermi level, is expected to exhibit novel electromagnetic phenomena. Although the large optical/electronic responses such as nonlinear optical effects and intrinsic anomalous Hall effect (AHE) have recently been demonstrated indeed, the conclusive evidence for their topological origins has remained elusive. Here, we report the gigantic magneto-optical (MO) response arising from the topological electronic structure with intense Berry curvature in magnetic WSM Co<sub>3</sub>Sn<sub>2</sub>S<sub>2</sub>. The low-energy MO spectroscopy and the first-principles calculation reveal that the interband transitions on the nodal rings connected to the Weyl points show the resonance of the optical Hall conductivity and give rise to the giant intrinsic AHE in dc limit. The terahertz Faraday and infrared Kerr rotations are found to be remarkably enhanced by these resonances with topological electronic structures, demonstrating the novel low-energy optical response inherent to the magnetic WSM.

      DOI: 10.1038/s41467-020-18470-0

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      その他リンク: http://www.nature.com/articles/s41467-020-18470-0

    • Stabilization of a honeycomb lattice of IrO6 octahedra by formation of ilmenite-type superlattices in MnTiO3 査読有り

      Kei Miura, Kohei Fujiwara, Kei Nakayama, Ryo Ishikawa, Naoya Shibata, Atsushi Tsukazaki

      Communications Materials1 ( 1 ) 55   2020年12月

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      担当区分:責任著者   掲載種別:研究論文(学術雑誌)   出版者・発行元:Springer Science and Business Media LLC  

      <title>Abstract</title>In quantum spin liquid research, thin films are an attractive arena that enables the control of magnetic interactions via epitaxial strain and two-dimensionality, which are absent in bulk crystals. Here, as a promising candidate for the development of quantum spin liquids in thin films, we propose a robust ilmenite-type oxide with a honeycomb lattice of edge-sharing IrO<sub>6</sub> octahedra artificially stabilised by superlattice formation using the ilmenite-type antiferromagnetic oxide MnTiO<sub>3</sub>. Stabilised sub-unit-cell-thick Mn–Ir–O layers are isostructural to MnTiO<sub>3</sub> and have an atomic arrangement corresponding to ilmenite-type MnIrO<sub>3</sub>. By performing spin Hall magnetoresistance measurements, we observe that antiferromagnetic ordering in the ilmenite Mn sublattice is suppressed by modified magnetic interactions in the MnO<sub>6</sub> planes via the IrO<sub>6</sub> planes. These findings contribute to the development of two-dimensional Kitaev candidate materials, accelerating the discovery of exotic physics and applications specific to quantum spin liquids.

      DOI: 10.1038/s43246-020-00059-1

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      その他リンク: http://www.nature.com/articles/s43246-020-00059-1

    • Insulator-to-Metal Transition of Cr2O3 Thin Films via Isovalent Ru3+ Substitution 査読有り 国際誌

      Kohei Fujiwara, Miho Kitamura, Daisuke Shiga, Yasuhiro Niwa, Koji Horiba, Tsutomu Nojima, Hiromichi Ohta, Hiroshi Kumigashira, Atsushi Tsukazaki

      Chemistry of Materials32 ( 12 ) 5272 - 5279   2020年5月27日

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      担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ACS Publications  

      DOI: 10.1021/acs.chemmater.0c01497

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    • Magnetic-field-induced topological phase transition in Fe-doped (Bi,Sb)2Se3 heterostructures 査読有り

      Y. Satake, J. Shiogai, G. P. Mazur, S. Kimura, S. Awaji, K. Fujiwara, T. Nojima, K. Nomura, S. Souma, T. Sato, T. Dietl, A. Tsukazaki

      Physical Review Materials4 ( 4 )   2020年4月21日

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      記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Physical Society (APS)  

      Three-dimensional topological insulators (3D TIs) possess a specific topological order of electronic bands, resulting in gapless surface states via bulk-edge correspondence. Exotic phenomena have been realized in ferromagnetic TIs, such as the quantum anomalous Hall (QAH) effect with a chiral-edge conduction and a quantized value of the Hall resistance R-yx. Here, we report on the emergence of distinct topological phases in paramagnetic Fe-doped (Bi,Sb)(2)Se-3 heterostructures with varying structure architecture, doping, and magnetic and electric fields. Starting from a 3D TI, a two-dimensional insulator appears at layer thicknesses below a critical value, which turns into an Anderson insulator for Fe concentrations sufficiently large to produce localization by magnetic disorder. With applying a magnetic field, a topological transition from the Anderson insulator to the QAH state occurs, which is driven by the formation of an exchange gap owing to a giant Zeeman splitting and reduced magnetic disorder. A topological phase diagram of (Bi,Sb)(2)Se-3 allows exploration of intricate interplay of topological protection, magnetic disorder, and exchange splitting.

      DOI: 10.1103/physrevmaterials.4.044202

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      その他リンク: https://link.aps.org/article/10.1103/PhysRevMaterials.4.044202

    • Anomalous Hall effect at the spontaneously electron-doped polar surface of PdCoO2 ultrathin films 査読有り

      T. Harada, K. Sugawara, K. Fujiwara, M. Kitamura, S. Ito, T. Nojima, K. Horiba, H. Kumigashira, T. Takahashi, T. Sato, A. Tsukazaki

      Physical Review Research2 ( 1 ) 013282   2020年3月9日

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      記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Physical Society (APS)  

      DOI: 10.1103/physrevresearch.2.013282

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      その他リンク: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevResearch.2.013282/fulltext

    • Signature of band inversion in the perovskite thin-film alloys BaSn1−xPbxO3 査読有り

      J. Shiogai, T. Chida, K. Hashimoto, K. Fujiwara, T. Sasaki, A. Tsukazaki

      Physical Review B101 ( 12 ) 125125   2020年3月

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      記述言語:英語   掲載種別:研究論文(学術雑誌)  

      DOI: 10.1103/PhysRevB.101.125125

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    • Electrical detection of the antiferromagnetic transition in MnTiO3 ultrathin films by spin Hall magnetoresistance 査読有り

      K. Miura, K. Fujiwara, J. Shiogai, T. Nojima, A.Tsukazaki

      Journal of Applied Physics127 ( 10 ) 103903   2020年3月

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      担当区分:責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)  

      DOI: 10.1063/1.5142193

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    • Doping-induced enhancement of anomalous Hall coefficient in Fe-Sn nanocrystalline films for highly sensitive Hall sensors 査読有り

      K. Fujiwara, Y. Satake, J. Shiogai, A. Tsukazaki

      APL Materials7 ( 11 ) 111103   2019年11月

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      担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)  

      DOI: 10.1063/1.5126499

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    • Low-frequency noise measurements on Fe-Sn Hall sensors 査読有り

      J. Shiogai, Z. Jin, Y. Satake, K. Fujiwara, A. Tsukazaki

      Applied Physics Express12 ( 12 ) 123001   2019年11月

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      記述言語:英語   掲載種別:研究論文(学術雑誌)  

      DOI: 10.7567/1882-0786/ab506a

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    • Ferromagnetic Co3Sn2S2 thin films fabricated by co-sputtering 査読有り

      K. Fujiwara, J. Ikeda, J. Shiogai, T. Seki, K. Takanashi, A. Tsukazaki

      Japanese Journal of Applied Physics58 ( 5 ) 050912   2019年4月

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      担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)  

      DOI: 10.7567/1347-4065/ab12ff

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    • Growth control of corundum-derivative MnSnO3 thin films by pulsed-laser deposition 査読有り

      K. Miura, K. Fujiwara, A. Tsukazaki

      AIP Advances9   035210   2019年3月

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      担当区分:責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)  

      DOI: 10.1063/1.5090407

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    • Fe-Sn nanocrystalline films for flexible magnetic sensors with high thermal stability 査読有り

      Y. Satake, K. Fujiwara, J. Shiogai, T. Seki, A. Tsukazaki

      Scientific Reports9   3282   2019年3月

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      担当区分:責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)  

      DOI: 10.1038/s41598-019-39817-8

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    • Formation of distorted rutile-type NbO2, MoO2, and WO2 films by reactive sputtering 査読有り

      K. Fujiwara, A. Tsukazaki

      Journal of Applied Physics125   085301   2019年2月

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      担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)  

      DOI: 10.1063/1.5079719

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    • Thin-film stabilization of LiNbO3-type ZnSnO3 and MgSnO3 by molecular-beam epitaxy 査読有り

      Kohei Fujiwara, Hiroya Minato, Junichi Shiogai, Akihito Kumamoto, Naoya Shibata, Atsushi Tsukazaki

      APL Materials7 ( 2 ) 022505   2019年2月1日

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      担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)  

      © 2018 Author(s). In polar crystals, cooperative ionic displacement produces a macroscopic spontaneous polarization. Among such polar materials, LiNbO 3 -type wide bandgap oxides are particularly appealing because they offer useful ferroelectric properties and also potentially lead to multiferroic materials. Using molecular-beam epitaxy, we investigated the thin-film growth of high-pressure phase LiNbO 3 -type ZnSnO 3 and discovered a polar oxide candidate, MgSnO 3 . We found that LiNbO 3 -type substrates play an essential role in the crystallization of these compounds, though corundum-type Al 2 O 3 substrates also have the identical crystallographic arrangement of oxygen sublattice. Optical transmittance and electrical transport measurements revealed their potential as a transparent conducting oxide. Establishment of a thin-film synthetic route would be the basis for exploration of functional polar oxides and research on conduction at ferroelectric interfaces and domain walls.

      DOI: 10.1063/1.5054289

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    • Improving resistance change with temperature and thermal stability in Fe3O4 films for high-temperature resistors 査読有り

      K. Fujiwara, S. Tsubota, H. Tanaka

      Applied Physics Express12   011003   2019年1月

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      担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)  

      DOI: 10.7567/1882-0786/aaf285

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    • Pulsed-laser deposition of InSe thin films for the detection of thickness-dependent bandgap modification 査読有り

      D. Zheng, J. Shiogai, K. Fujiwara, A. Tsukazaki

      Applied Physics Letters113 ( 25 ) 253501   2018年12月

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      記述言語:英語   掲載種別:研究論文(学術雑誌)  

      DOI: 10.1063/1.5064736

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    • Effect of the depletion region in topological insulator heterostructures for ambipolar field-effect transistors 査読有り

      Satake Yosuke, Shiogai Junichi, Fujiwara Kohei, Tsukazaki Atsushi

      PHYSICAL REVIEW B98 ( 12 )   2018年9月20日

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      記述言語:英語   掲載種別:研究論文(学術雑誌)  

      DOI: 10.1103/PhysRevB.98.125415

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    • High-mobility field-effect transistor based on crystalline ZnSnO3 thin films 査読有り

      Hiroya Minato, Kohei Fujiwara, Atsushi Tsukazaki

      AIP Advances8 ( 5 ) 055327-1 - 055327-6   2018年5月1日

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      担当区分:責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Institute of Physics Inc.  

      We propose crystalline ZnSnO3 as a new channel material for field-effect transistors. By molecular-beam epitaxy on LiNbO3(0001) substrates, we synthesized films of ZnSnO3, which crystallizes in the LiNbO3-type polar structure. Field-effect transistors on ZnSnO3 exhibit n-type operation with field-effect mobility of as high as 45 cm2V-1s-1 at room temperature. Systematic examination of the transistor operation for channels with different Zn/Sn compositional ratios revealed that the observed high-mobility reflects the nature of stoichiometric ZnSnO3 phase. Moreover, we found an indication of coupling of transistor characteristics with intrinsic spontaneous polarization in ZnSnO3, potentially leading to a distinct type of polarization-induced conduction.

      DOI: 10.1063/1.5034403

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    • Highly conductive PdCoO2 ultrathin films for transparent electrodes 査読有り

      T. Harada, K. Fujiwara, A. Tsukazaki

      APL Materials6 ( 4 ) 046107-1 - 046107-6   2018年4月1日

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      記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Institute of Physics Inc.  

      We report on the successful synthesis of highly conductive PdCoO2 ultrathin films on Al2O3 (0001) by pulsed laser deposition. The thin films grow along the c-axis of the layered delafossite structure of PdCoO2, corresponding to the alternating stacking of conductive Pd layers and CoO2 octahedra. The thickness-dependent transport measurement reveals that each Pd layer has a homogeneous sheet conductance as high as 5.5 mS in the samples thicker than the critical thickness of 2.1 nm. Even at the critical thickness, high conductivity exceeding 104 S cm-1 is achieved. Optical transmittance spectra exhibit high optical transparency of PdCoO2 thin films particularly in the near-infrared region. The concomitant high values of electrical conductivity and optical transmittance make PdCoO2 ultrathin films promising transparent electrodes for triangular-lattice-based materials.

      DOI: 10.1063/1.5027579

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    • Enhancement of superconducting transition temperature in FeSe electric-double-layer transistor with multivalent ionic liquids 査読有り

      Miyakawa Tomoki, Shiogai Junichi, Shimizu Sunao, Matsumoto Michio, Ito Yukihiro, Harada Takayuki, Fujiwara Kohei, Nojima Tsutomu, Itoh Yoshimitsu, Aida Takuzo, Iwasa Yoshihiro, Tsukazaki Atsushi

      PHYSICAL REVIEW MATERIALS2 ( 3 )   2018年3月26日

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      記述言語:英語   掲載種別:研究論文(学術雑誌)  

      DOI: 10.1103/PhysRevMaterials.2.031801

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    • Fermi-level tuning of the Dirac surface state in (Bi1-xSbx)2Se3 thin films 査読有り

      Yosuke Satake, Junichi Shiogai, Daichi Takane, Keiko Yamada, Kohei Fujiwara, Seigo Souma, Takafumi Sato, Takashi Takahashi, Atsushi Tsukazaki

      Journal of Physics Condensed Matter30 ( 8 )   2018年2月1日

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      記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Institute of Physics Publishing  

      We report on the electronic states and the transport properties of three-dimensional topological insulator (Bi1-xSbx)2Se3 ternary alloy thin films grown on an isostructural Bi2Se3 buffer layer on InP substrates. By angle-resolved photoemission spectroscopy, we clearly detected Dirac surface states with a large bulk band gap of 0.2-0.3 eV in the (Bi1-xSbx)2Se3 film with x = 0.70. In addition, we observed by Hall effect measurements that the dominant charge carrier converts from electron (n-type) to hole (p-type) at around x = 0.7, indicating that the Fermi level can be controlled across the Dirac point. Indeed, the carrier transport was shown to be governed by Dirac surface state in 0.63 x 0.75. These features suggest that Fermi-level tunable (Bi1-xSbx)2Se3-based heterostructures provide a platform for extracting exotic topological phenomena.

      DOI: 10.1088/1361-648X/aaa724

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    • Fabrication of tetragonal FeSe – FeS alloy films with high sulfur contents by alternate deposition 査読有り

      K. Fujiwara, J. Shiogai, A. Tsukazaki

      Jpn. J. Appl. Phys.56 ( 10 ) 100308 - 100308   2017年9月19日

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      担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Institute of Physics  

      We report the synthesis of tetragonal FeS<inf>x</inf>Se<inf>1−</inf><inf>x</inf>films (x ≤ 0.78) by pulsed-laser deposition. To fabricate tetragonal alloy films with tetragonal FeSe and hexagonal FeS targets, we adopted an alternate deposition technique with an FeSe buffer layer on MgO(001). The overall film composition is controlled by the thickness ratio of FeS/FeSe layers. The out-of-plane lattice parameter of the films follows Vegard’s law, demonstrating homogeneous alloying by interdiffusion. The sulfur solid solubility reaches x = 0.78 in the FeS<inf>x</inf>Se<inf>1−</inf><inf>x</inf>films, which is by far higher than x ∼ 0.40 in bulk governed by the tetragonal phase instability.

      DOI: 10.7567/JJAP.56.100308.

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    • Enhanced electron mobility at the two-dimensional metallic surface of BaSnO3 electric-double-layer transistor at low temperatures 査読有り

      Kohei Fujiwara, Kazuki Nishihara, Junichi Shiogai, Atsushi Tsukazaki

      APPLIED PHYSICS LETTERS110 ( 20 ) 203503   2017年5月

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      担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER INST PHYSICS  

      Wide-bandgap oxides exhibiting high electron mobility hold promise for the development of useful electronic and optoelectronic devices as well as for basic research on two-dimensional electron transport phenomena. A perovskite-type tin oxide, BaSnO3, is currently one of such targets owing to distinctly high mobility at room temperature. The challenge to overcome towards the use of BaSnO3 thin films in applications is suppression of dislocation scattering, which is one of the dominant scattering origins for electron transport. Here, we show that the mobility of the BaSnO3 electric-double-layer transistor reaches 300 cm(2) V-1 s(-1) at 50 K. The improved mobility indicates that charged dislocation scattering is effectively screened by electrostatically doped high-density charge carriers. We also observed metallic conduction persisting down to 2 K, which is attributed to the transition to the degenerate semiconductor. The experimental verification of bulk-level mobility at the densely accumulated surface sheds more light on the importance of suppression of dislocation scattering by interface engineering in doped BaSnO3 thin films for transparent electrode applications. Published by AIP Publishing.

      DOI: 10.1063/1.4983611

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    • High field-effect mobility at the (Sr,Ba)SnO3/BaSnO3 interface 査読有り

      Kohei Fujiwara, Kazuki Nishihara, Junichi Shiogai, Atsushi Tsukazaki

      AIP ADVANCES6 ( 8 ) 085014   2016年8月

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      担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER INST PHYSICS  

      A perovskite oxide, BaSnO3, has been classified as one of transparent conducting materials with high electron mobility, and its application for field-effect transistors has been the focus of recent research. Here we report transistor operation in BaSnO3-based heterostructures with atomically smooth surfaces, fabricated on SrTiO3 substrates by the (Sr,Ba)SnO3 buffer technique. Indeed, modulation of band profiles at the channel interfaces with the insertion of wide bandgap (Sr,Ba)SnO3 as a barrier layer results in a significant improvement of field-effect mobility, implying effective carrier doping at the regulated heterointerface. These results provide an important step towards realization of high-performance BaSnO3-based field-effect transistors. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

      DOI: 10.1063/1.4961637

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    • Electric field-induced transport modulation in VO2 FETs with high-k oxide/organic parylene-C hybrid gate dielectric 査読有り

      Tingting Wei, Teruo Kanki, Kohei Fujiwara, Masashi Chikanari, Hidekazu Tanaka

      APPLIED PHYSICS LETTERS108 ( 5 ) 034502   2016年2月

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

      We report on the observation of reversible and immediate resistance switching by high-k oxide Ta2O5/organic parylene-C hybrid dielectric-gated VO2 thin films. Resistance change ratios at various temperatures in the insulating regime were demonstrated to occur in the vicinity of phase transition temperature. We also found an asymmetric hole-electron carrier modulation related to the suppression of phase transition temperature. The results in this research provide a possibility for clarifying the origin of metal-insulator transition in VO2 through the electrostatic field-induced transport modulation. (C) 2016 AIP Publishing LLC.

      DOI: 10.1063/1.4941233

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    • Impact of parylene-C thickness on performance of KTaO3 field-effect transistors with high-k oxide/parylene-C hybrid gate dielectric 査読有り

      Tingting Wei, Kohei Fujiwara, Teruo Kanki, Hidekazu Tanaka

      JOURNAL OF APPLIED PHYSICS119 ( 3 ) 034502   2016年1月

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

      The proposal of a hybrid gate dielectric systematically modulated with low-k material layer has been shown to be a promising strategy in the development of low-consumption field-effect transistors (FETs) with high performance. In this work, by fabricating KTaO3 FETs containing Y-doped Ta2O5/parylene-C hybrid gate dielectrics with different ratios of component thicknesses, we explored the dependence of the transistor electrical properties on the parylene-C layer thickness. Based on the results and analysis, an optimized transistor performance was achieved with an appropriate Y-doped Ta2O5/parylene-C thickness ratio from the point of view on low voltage operation. This study contributes to provide guidance for future device design and applications. (c) 2016 AIP Publishing LLC.

      DOI: 10.1063/1.4940387

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    • Discrimination between gate-induced electrostatic and electrochemical characteristics in insulator-to-metal transition of manganite thin films 査読有り

      Takuro Nakamura, Azusa N. Hattori, Thi Van Anh Nguyen, Kohei Fujiwara, Hidekazu Tanaka

      APPLIED PHYSICS EXPRESS8 ( 7 ) 073201   2015年7月

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      記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IOP PUBLISHING LTD  

      We propose a method of discriminating whether the gating effect is electrostatic or electrochemical on an electric double-layer transistor (EDLT), which can be a good guideline for examining the nature of EDLTs. The electrochemical effect between a channel and an ionic liquid depends on the gate voltage (V-G). Our study on the dependence of the transport properties of a (La0.525Pr0.1Ca0.375)MnO3 (LPCMO) EDLT on V-G revealed that the electrostatic effect is dominant below vertical bar V-G vertical bar = 2 V, whereas the electrochemical effect is dominant at higher voltages. The modulation of the insulator-to-metal transition property of LPCMO was realized through the electrostatic effect. (C) 2015 The Japan Society of Applied Physics

      DOI: 10.7567/APEX.8.073201

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    • Identification of Giant Mott Phase Transition of Single Electric Nanodomain in Manganite Nanowall Wire 査読有り

      Azusa N. Hattori, Yasushi Fujiwara, Kohei Fujiwara, Thi Van Anh Nguyen, Takuro Nakamura, Masayoshi Ichimiya, Masaaki Ashida, Hidekazu Tanaka

      NANO LETTERS15 ( 7 ) 4322 - 4328   2015年7月

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

      In the scaling down of electronic devices, functional oxides with strongly correlated electron system provide advantages to conventional semiconductors, namely, huge switching owing to their phase transition and high carrier density, which guarantee their rich functionalities even at the 10 nm scale. However, understanding how their functionalities behave at a scale of 10 nm order is still a challenging issue. Here, we report the construction of the well-defined (La,Pr,Ca)MnO3 epitaxial oxide nanowall wire by combination of nanolithography and subsequent thin-film growth, which allows the direct investigation of its insulator-metal transition (IMT) at the single domain scale. We show that the width of a (La,Pr,Ca)MnO3 nanowall sample can be reduced to 50 nm, which is smaller than the observed 70-200 nm-size electronic domains, and that a single electronic nanodomain in (La,Pr,Ca)MnO3 exhibited an intrinsic first-order IMT with an unusually steep single-step change in its magnetoresistance and temperature-induced resistance due to the domains arrangement in series. A simple model of the first-order transition for single electric domains satisfactorily illustrates the IMT behavior from macroscale down to the nanoscale.

      DOI: 10.1021/acs.nanolett.5b00264

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    • 3D-architected and integrated metal oxide nanostructures and beyond produced by three-dimensional nanotemplate pulsed laser deposition 査読有り

      Azusa N. Hattori, Yasushi Fujiwara, Kohei Fujiwara, Hidekazu Tanaka

      e-Journal of Surface Science and Nanotechnology13   279 - 283   2015年6月6日

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      記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:Surface Science Society of Japan  

      A novel nanofabrication technique, namely three-dimensional (3D) nanotemplate pulsed laser deposition, that can typically be useful for metal oxides has been developed by combining inclined pulsed laser deposition with a 3D nanotemplate prepared by nanoimprint lithography. This method enables the production of size-adjustable and extremely small functional oxide nanostructures with a high packing density over a large area, with high controllability of their shape, location, and alignment. We report various 3D functional metal oxide nanostructures, such as a luminescent ZnO nanobox structure, a ferromagnetic semiconductor (Fe,Zn)&lt
      inf&gt
      3&lt
      /inf&gt
      O&lt
      inf&gt
      4&lt
      /inf&gt
      nanobox structure, an (Fe,Mn)&lt
      inf&gt
      3&lt
      /inf&gt
      O&lt
      inf&gt
      4&lt
      /inf&gt
      epitaxial nanowall wire structure, and an in-plane metal-oxide-semiconductor hetero epitaxial nanowire structure. These nanostructures should be good candidates for optoelectronic, spintronic, and electronic nanoscale device applications.

      DOI: 10.1380/ejssnt.2015.279

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    • Estimation of dc transport dynamics in strongly correlated (La,Pr,Ca)MnO3 film using an insulator-metal composite model for terahertz conductivity 査読有り

      T. V. A. Nguyen, A. N. Hattori, M. Nagai, T. Nakamura, K. Fujiwara, M. Ashida, H. Tanaka

      APPLIED PHYSICS LETTERS105 ( 2 ) 023502   2014年7月

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

      Temperature-dependent conductivities at dc and terahertz (THz) frequency region (sigma(THz)(omega,T)) were obtained for a strongly correlated (La0.275Pr0.35Ca0.375)MnO3 (LPCMO) film using THz time domain spectroscopy. A composite model that describes sigma(THz)(omega,T) for LPCMO through the insulator-metal transition (IMT) was established by incorporating Austin-Mott model characterizing the hopping of localized electrons and Drude model explaining the behavior of free electrons. This model enables us to reliably investigate the dc transport dynamics from THz conductivity measurement, i.e., simultaneously evaluate the dc conductivity and the competing composition of metal and insulator phases through the IMT, reflecting the changes in microscopic conductivity of these phases. (C) 2014 AIP Publishing LLC.

      DOI: 10.1063/1.4890109

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    • Dual field effects in electrolyte-gated spinel ferrite: electrostatic carrier doping and redox reactions 査読有り

      Takashi Ichimura, Kohei Fujiwara, Hidekazu Tanaka

      SCIENTIFIC REPORTS4   5818   2014年7月

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      記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:NATURE PUBLISHING GROUP  

      Controlling the electronic properties of functional oxide materials via external electric fields has attracted increasing attention as a key technology for next-generation electronics. For transition-metal oxides with metallic carrier densities, the electric-field effect with ionic liquid electrolytes has been widely used because of the enormous carrier doping capabilities. The gate-induced redox reactions revealed by recent investigations have, however, highlighted the complex nature of the electric-field effect. Here, we use the gate-induced conductance modulation of spinel ZnxFe3-xO4 to demonstrate the dual contributions of volatile and non-volatile field effects arising from electronic carrier doping and redox reactions. These two contributions are found to change in opposite senses depending on the Zn content x; virtual electronic and chemical field effects are observed at appropriate Zn compositions. The tuning of field-effect characteristics via composition engineering should be extremely useful for fabricating high-performance oxide field-effect devices.

      DOI: 10.1038/srep05818

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    • Nonvolatile Transport States in Ferrite Thin Films Induced by Field-Effect Involving Redox Processes 査読有り

      Kohei Fujiwara, Takashi Ichimura, Hidekazu Tanaka

      ADVANCED MATERIALS INTERFACES1 ( 3 ) 1300108   2014年6月

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      担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:WILEY-BLACKWELL  

      DOI: 10.1002/admi.201300108

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    • Electrical switching to probe complex phases in a frustrated manganite 査読有り

      Saket Asthana, Kohei Fujiwara, Hidekazu Tanaka

      SOLID STATE COMMUNICATIONS187   64 - 67   2014年6月

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      記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

      Electrical switching was used to investigate complex phases induced by Cr-substitution in (Pr1/3Sm2/3)(2/3) Sr1/3MnO3. This system was expected to transform from a Type I (Mn4+/Mn3+ approximate to 3/7) to Type II (Mn4+/Mn3+ approximate to 1) manganite at critical Cr content, satisfying a virtual Mn4+/Mn3+ ratio close to unity. The phase diagram of (Pr1/3Sm2/3)(2/3)Sr1/3Mn0.8Cr0.2O3 including charge/spin ordered/disordered phases was probed by electrical switching. The ferromagnetic insulating phase at &lt; similar to 100 K, located next to the charge-ordered antiferromagnetic phase, exhibited a sudden use in conductivity upon electric-held biasing. This resulted from the melting or charge ordering, and demonstrated the presence or a crossover regime or two coexisting magnetic orderings. (C) 2014 Elsevier Ltd. All rights reserved.

      DOI: 10.1016/j.ssc.2014.02.014

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    • Artificial three dimensional oxide nanostructures for high performance correlated oxide nanoelectronics 査読有り

      Hidekazu Tanaka, Hidefumi Takami, Teruo Kanki, Azusa N. Hattori, Kohei Fujiwara

      JAPANESE JOURNAL OF APPLIED PHYSICS53 ( 5 ) 05FA10   2014年5月

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      記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IOP PUBLISHING LTD  

      We report a strategy for controlling nanoscopic electronic domains to produce gigantic Mott metal-insulator transition phenomena in strongly correlated oxides by fabricating oxide micro-nano-wires, nanowalls, nanoboxes. We investigated the dependence of spatial dimensionality on wire width for a disordered configurations of metallic domains in VO2 microwires to nanowires on TiO2(001) and Al2O3(0001) substrates with well-positioned alignment by a nanoimprint (NIL) technique. We observed a temperature-induced steep multistep metal-insulator transition in artificial VO2 micro/nano-wires. With further development, we report a new bottom-up fabrication method for the formation of extremely small transition-metal oxide nanostructures employing a combination of NIL and pulsed laser deposition (PLD) techniques, called the three-dimensional nanotemplate-PLD method, to demonstrate functional oxide nanowall wires, nanoboxes, and hetero-nanowall oxide devices with widths of 20-120nm and excellent size controllability. (C) 2014 The Japan Society of Applied Physics

      DOI: 10.7567/JJAP.53.05FA10

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    • Fabrication of three-dimensional epitaxial (Fe,Zn)(3)O-4 nanowall wire structures and their transport properties 査読有り

      Azusa N. Hattori, Yasushi Fujiwara, Kohei Fujiwara, Yasukazu Murakami, Daisuke Shindo, Hidekazu Tanaka

      APPLIED PHYSICS EXPRESS7 ( 4 ) 045201   2014年4月

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      記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IOP PUBLISHING LTD  

      We have established a unique technique to fabricate three-dimensional (3D) well-defined transition-metal oxide epitaxial nanostructures. Fabrication of epitaxial spinel ferrite Fe2.2Zn0.8O4 (FZO) nanowall wires with a tunable width down to 20 nm was achieved. Cross-sectional transmission electron microscopy revealed the existence of an epitaxially matched lateral interface between the FZO nanowall wire and the side surface of 3D-MgO substrate. Magnetoresistance measurements showed ferromagnetic properties of the FZO nanowall wire at 300 K. The role of antiphase boundaries on the functionalities of the FZO nanoconfined wire is discussed. (C) 2014 The Japan Society of Applied Physics

      DOI: 10.7567/APEX.7.045201

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    • 5d iridium oxide as a material for spin-current detection 査読有り

      Kohei Fujiwara, Yasuhiro Fukuma, Jobu Matsuno, Hiroshi Idzuchi, Yasuhiro Niimi, YoshiChika Otani, Hidenori Takagi

      NATURE COMMUNICATIONS4   2893   2013年12月

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      担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:NATURE PUBLISHING GROUP  

      Devices based on pure spin currents have been attracting increasing attention as key ingredients for low-dissipation electronics. To integrate such spintronics devices into charge-based technologies, electric detection of spin currents is essential. The inverse spin Hall effect converts a spin current into an electric voltage through spin-orbit coupling. Noble metals such as Pt and Pd, and also Cu-based alloys, have been regarded as potential materials for a spin-current injector, owing to the large direct spin Hall effect. Their spin Hall resistivity rho(SH), representing the performance as a detector, is not large enough, however, due mainly because of their low charge resistivity. Here we report that a binary 5d transition metal oxide, iridium oxide, overcomes the limitations encountered in noble metals and Cu-based alloys and shows a very large rho(SH)similar to 38 mu Omega cm at room temperature.

      DOI: 10.1038/ncomms3893

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    • Observation of rebirth of metallic paths during resistance switching of metal nanowire 査読有り

      K. Horiba, K. Fujiwara, N. Nagamura, S. Toyoda, H. Kumigashira, M. Oshima, H. Takagi

      APPLIED PHYSICS LETTERS103 ( 19 ) 193114   2013年11月

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

      To clarify the mechanism of resistance-switching phenomena, we have investigated the change in the electronic structure of a Ni nanowire device during resistance-switching operations using scanning photoelectron microscopy techniques. We directly observed the disappearance of density of state (DOS) at the Fermi level (E-F) in a high-resistance state and recovery of a finite DOS at E-F in a low-resistance state. These results are direct evidence that the Ni nanowire is fully oxidized after switching to the high-resistance state and that Ni-metal conductive paths in the oxidized nanowire are recovered in the low-resistance state. (C) 2013 AIP Publishing LLC.

      DOI: 10.1063/1.4829469

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    • Unstrained Epitaxial Zn-Substituted Fe3O4 Films for Ferromagnetic Field-Effect Transistors 査読有り

      Takashi Ichimura, Kohei Fujiwara, Takayoshi Kushizaki, Teruo Kanki, Hidekazu Tanaka

      JAPANESE JOURNAL OF APPLIED PHYSICS52 ( 6 ) UNSP 068002   2013年6月

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      記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:JAPAN SOC APPLIED PHYSICS  

      A field-effect transistor has been fabricated utilizing an epitaxial film of unstrained zinc-substituted magnetite (Fe3O4) as the active channel. A thin film of Fe2.5Zn0.5O4 was grown on a lattice-matched MgO(001) substrate by pulsed-laser deposition and covered by a parylene gate insulator to dope charge carriers by a field effect. The device showed a field-effect mobility of 1.2 x 10(-2) cm(2) V-1 s(-1) at 300 K, which is higher by a factor of 15 than those of the devices with strained Fe2.5Zn0.5O4 channels on perovskite-type substrates. The enhanced response to the gate electric field is useful in exploring gate-tunable magnetism in magnetite. (C) 2013 The Japan Society of Applied Physics

      DOI: 10.7567/JJAP.52.068002

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    • Electric-field breakdown of the insulating charge-ordered state in LuFe2O4 thin films 査読有り

      Kohei Fujiwara, Tatsuya Hori, Hidekazu Tanaka

      JOURNAL OF PHYSICS D-APPLIED PHYSICS46 ( 15 ) 155108   2013年4月

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      記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IOP PUBLISHING LTD  

      We have studied the dielectric breakdown of the insulating charge-ordered state and the associated current switching phenomenon in layered ferrite LuFe2O4. To elucidate the correlation between the ordering pattern and current switching behaviour, we synthesized highly c-axis oriented thin films by pulsed-laser deposition. An enhanced switching effect was achieved in the three-dimensional charge-ordered phase below similar to 310 K, but not in the high-temperature two-dimensional phase. High-field transport measurements revealed that collective depinning of localized charge carriers is essential to induce switching. The lack of collective charge motion is proposed as the origin of the switching suppression in the two-dimensional phase.

      DOI: 10.1088/0022-3727/46/15/155108

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    • In-Plane Oblique Pulsed-Laser Deposition and Its Application to the Fabrication of Metal Oxide Nanoconstrictions 査読有り

      Takayoshi Kushizaki, Kohei Fujiwara, Yasushi Fujiwara, Azusa N. Hattori, Hidekazu Tanaka

      APPLIED PHYSICS EXPRESS6 ( 3 ) 035201   2013年3月

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      記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:JAPAN SOC APPLIED PHYSICS  

      We propose a novel approach to fabricate metal oxide nanostructures with locally modified thicknesses. Utilizing a nanoscale shadowing effect induced by a three-dimensional nanotemplate patterned on a substrate, we demonstrate that pulsed-laser deposition in an in-plane oblique configuration enables us to locally grow an oxide. The analysis on the growth position reveals that it can be precisely defined by adjusting only a few geometrical parameters. A ferromagnetic oxide Fe2.5Zn0.5O4 nanoconstriction with a bottleneck width of 65nm and a length of 53nm is fabricated by controlling the incident azimuthal angle and growth duration in sequential deposition processes. (C) 2013 The Japan Society of Applied Physics

      DOI: 10.7567/APEX.6.035201

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    • Nanowall-Shaped MgO Substrate with Flat (100) Sidesurface: A New Route to Three-Dimensional Functional Oxide Nanostructured Electronics 査読有り

      Yasushi Fujiwara, Azusa N. Hattori, Kohei Fujiwara, Hidekazu Tanaka

      JAPANESE JOURNAL OF APPLIED PHYSICS52 ( 1 ) 015001   2013年1月

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      記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:JAPAN SOC APPLIED PHYSICS  

      An architecturally designed nanowall-shaped MgO (nanowall MgO) was fabricated by the combination of nanoimprint lithography (NIL) and pulsed-laser deposition (PLD). The sidesurface on the nanowall MgO exhibited (111) facets with edge truncation instead of the most stable (100) face when the aspect ratio between the height and width of the nanowall MgO was lower than 0.7. By optimizing the surface crystallography, typically by designing the nanowall aspect ratio and controlling the postannealing treatment conditions, nanowall MgO with a single-crystal flat (100) sidesurface could be produced. Applying the nanowall MgO to a substrate, we demonstrated the formation of extremely small three-dimensional (3D) epitaxial metal oxide nanostructures with an arbitrarily controlled size. The nanofabrication technique utilizing the nanowall MgO substrate will open a new route to high-quality 3D epitaxial metal oxide nanostructures. (C) 2013 The Japan Society of Applied Physics

      DOI: 10.7567/JJAP.52.015001

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    • Controlled fabrication of artificial ferromagnetic (Fe, Mn)(3)O-4 nanowall-wires by a three-dimensional nanotemplate pulsed laser deposition method 査読有り

      Takayoshi Kushizaki, Kohei Fujiwara, Azusa N. Hattori, Teruo Kanki, Hidekazu Tanaka

      NANOTECHNOLOGY23 ( 48 ) 485308   2012年12月

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      記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IOP PUBLISHING LTD  

      We have developed a new method to fabricate extremely small transition-metal oxide nanowires. Using a combination of nanoimprint template patterning and inclined substrate pulsed laser deposition, we successfully fabricated magnetic oxide Fe2.5Mn0.5O4 nanowall-wires, and controlled the width in a range from 120 nm down to about 20 nm by varying deposition parameters. Magnetoresistance measurements revealed ferromagnetic properties of the Fe2.5Mn0.5O4 nanowall-wire. This method enables the study of mesoscopic transport properties of transition-metal oxides towards the development of oxide-based nanodevices.

      DOI: 10.1088/0957-4484/23/48/485308

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    • Tuning metal-insulator transition by one dimensional alignment of giant electronic domains in artificially size-controlled epitaxial VO2 wires 査読有り

      Hidefumi Takami, Kenichi Kawatani, Hiroki Ueda, Kohei Fujiwara, Teruo Kanki, Hidekazu Tanaka

      APPLIED PHYSICS LETTERS101 ( 26 ) 263111   2012年12月

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

      We demonstrate control of spatial dimensionality of disordered configurations of giant electronic domains in systematically size-changed VO2 wires on TiO2 (001) substrates. One-dimensional alignment of the domains appears in wires narrower than 15 mu m width, while two-dimensional configurations were observed for larger ones. The rearrangement of domains from two to one dimension causes modification of electronic properties. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4773371]

      DOI: 10.1063/1.4773371

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    • Three dimensional nano-seeding assembly of ferromagnetic Fe/LaSrFeO4 nano-hetero dot array 査読有り

      K. Okada, T. Sakamoto, K. Fujiwara, A. N. Hattori, T. Kanki, H. Tanaka

      JOURNAL OF APPLIED PHYSICS112 ( 2 ) 024320   2012年7月

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

      Well-ordered ferromagnetic Fe nanodots/LaSrFeO4 nanocomposites have been fabricated by self-assembled crystal growth on La-SrTiO3 substrates having Fe nanoseed array fabricated by nanoimprint lithography (NIL). The Fe nanoseeds with spacing of 200 nm make possible the formation of perfectly arranged Fe/LaSrFeO4 nanocomposites; phase-separated Fe nanodots and the LaSrFeO4 matrix grew only on the nanoseeds and on the area except nanoseeds, respectively. A calculation based on a surface diffusion model has indicated that the nanoseed spacing required for the formation of the perfectly arranged nanocomposite is less than 400 nm. Magnetic force microscopy revealed an arrangement of isolated ferromagnetic domain corresponding to Fe nanodots grown on the Fe nanoseeds. The combination of self-assembled growth and NIL gives a route of the rational formation of high-density ferromagnetic memory devices. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4739719]

      DOI: 10.1063/1.4739719

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    • Spatial Redistribution of Oxygen Ions in Oxide Resistance Switching Device after Forming Process 査読有り

      Takeshi Yajima, Kohei Fujiwara, Aiko Nakao, Tomohiro Kobayashi, Toshiyuki Tanaka, Kei Sunouchi, Yoshiaki Suzuki, Mai Takeda, Kentaro Kojima, Yoshinobu Nakamura, Kouji Taniguchi, Hidenori Takagi

      JAPANESE JOURNAL OF APPLIED PHYSICS49 ( 6 ) 060215   2010年6月

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      記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:JAPAN SOC APPLIED PHYSICS  

      The change in the spatial distribution of oxygen ions after an initial voltage application called the forming process was investigated for oxide resistance switching devices by secondary ion mass spectrometry mapping. To track the motion of oxygen ions, tracer (18)O ions were implanted in a planar Pt/CuO/Pt device. We found clear evidence for the oxygen reduction in the conductive bridge structure formed between two electrodes. In addition, the oxygen ions in the bridge structure drift to the anode, implying the oxygen diffusion (migration) induced by high electric field and/or current density. We discuss those results in terms of a filament model. (C) 2010 The Japan Society of Applied Physics

      DOI: 10.1143/JJAP.49.060215

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    • V-V dimerization effects on bulk-sensitive hard x-ray photoemission spectra for Magneacuteli phase vanadium oxides 査読有り

      M. Obara, A. Sekiyama, S. Imada, J. Yamaguchi, T. Miyamachi, T. Balashov, W. Wulfhekel, M. Yabashi, K. Tamasaku, A. Higashiya, T. Ishikawa, K. Fujiwara, H. Takagi, S. Suga

      PHYSICAL REVIEW B81 ( 11 ) 113107   2010年3月

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

      Highly bulk-sensitive hard x-ray photoemission has been performed for the Magneacuteli phase V(5)O(9) and V(6)O(11), which are composed of V(2)O(3) and VO(2) from chemical point of view. The valence-band spectra near the Fermi level are rather similar between V(5)O(9) and V(6)O(11) in both metallic and insulating phases. Although the core-level spectra in the metallic phase are similar between V(5)O(9) and V(6)O(11), the core-level spectra in the insulating phase are noticeably different. Our results are understood by considering the contribution of the V-V dimerization effects, which are strong in V(6)O(11) and negligible in V(5)O(9). Comparison of the core-level spectra of V(5)O(9) and V(6)O(11) with those of VO(2) has revealed that the mechanism of the metal-insulator transitions for the former two compounds is different from that for VO(2).

      DOI: 10.1103/PhysRevB.81.113107

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    • Anomalous State Sandwiched between Fermi Liquid and Charge Ordered Mott-Insulating Phases of Ti4O7 査読有り

      M. Taguchi, A. Chainani, M. Matsunami, R. Eguchi, Y. Takata, M. Yabashi, K. Tamasaku, Y. Nishino, T. Ishikawa, S. Tsuda, S. Watanabe, C. -T. Chen, Y. Senba, H. Ohashi, K. Fujiwara, Y. Nakamura, H. Takagi, S. Shin

      PHYSICAL REVIEW LETTERS104 ( 10 ) 106401   2010年3月

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

      The Magneli phase Ti4O7 exhibits two sharp jumps in resistivity with coupled structural transitions as a function of temperature at T-c1 similar to 142 K and T-c2 = 154 K. We have studied electronic structure changes across the two transitions using 7 eV laser, soft x-ray, and hard x-ray (HX) photoemission spectroscopy (PES). Ti 2p - 3d resonant PES and HX PES show a clear metallic Fermi edge and mixed valency above T-c2. The low temperature phase below T-c1 shows a clear insulating gap of similar to 100 meV. The intermediate phase between T-c1 and T-c2 indicates a pseudogap coexisting with remnant coherent states. HX PES and complementary calculations have confirmed the coherent screening in the strongly correlated intermediate phase. The results suggest the existence of a highly anomalous state sandwiched between the mixed-valent Fermi liquid and charge ordered Mott-insulating phase in Ti4O7.

      DOI: 10.1103/PhysRevLett.104.106401

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    • Electrode-Geometry Control of the Formation of a Conductive Bridge in Oxide Resistance Switching Devices 査読有り

      Kohei Fujiwara, Takeshi Yajima, Yoshinobu Nakamura, Marcelo J. Rozenberg, Hidenori Takagi

      APPLIED PHYSICS EXPRESS2 ( 8 ) 081401   2009年8月

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      担当区分:最終著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:JAPAN SOCIETY APPLIED PHYSICS  

      Control of the formation of conductive bridge between the metal electrodes in planar-type resistance switching device was attempted. We demonstrated in Pt/CuO/Pt devices that, using a triangular seed electrode for soft breakdown, the position and the size of the bridge can be controlled. The decrease in the size resulted in the drastic reduction of operation voltage and current to the same level as in capacitor-type stacked device. We argue that the planar-type device might have a certain advantage for future non-volatile memory application. (C) 2009 The Japan Society of Applied Physics

      DOI: 10.1143/APEX.2.081401

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    • Inhomogeneous chemical states in resistance-switching devices with a planar-type Pt/CuO/Pt structure 査読有り

      R. Yasuhara, K. Fujiwara, K. Horiba, H. Kumigashira, M. Kotsugi, M. Oshima, H. Takagi

      APPLIED PHYSICS LETTERS95 ( 1 ) 012110   2009年7月

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

      The spatial distribution of chemical states in resistance-switching devices with a planar-type Pt/CuO/Pt structure has been studied by photoemission electron microscopy. It has been found that the change in resistance that occurs with the application of the first voltage is caused by the formation of a reduction path through the CuO channel between the Pt electrodes. A detailed analysis suggests that Joule-heat-assisted reduction induced by the current flowing through the device may play an important role in the formation of the conductive reduction path. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3175720]

      DOI: 10.1063/1.3175720

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    • Resistance Switching and Formation of a Conductive Bridge in Metal/Binary Oxide/Metal Structure for Memory Devices 査読有り

      Kohei Fujiwara, Takumi Nemoto, Marcelo J. Rozenberg, Yoshinobu Nakamura, Hidenori Takagi

      JAPANESE JOURNAL OF APPLIED PHYSICS47 ( 8 ) 6266 - 6271   2008年8月

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      担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:JAPAN SOCIETY APPLIED PHYSICS  

      The resistance switching mechanism of a metal/CuO/metal sandwich with a planar device structure has been studied. We report the direct observation of a conducting bridge within the CuO channel of the device, which is formed upon the initial voltage application (forming process). It is found that the resistance switching phenomenon only occurs when just a single bridge is formed during a soft dielectric breakdown. We argue that the reduction and oxidation of this conducting bridge by the action of an applied field and/or current gives rise to a novel nonvolatile memory effect.

      DOI: 10.1143/JJAP.47.6266

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    • Accumulation and depletion layer thicknesses in organic field effect transistors 査読有り

      M Kiguchi, M Nakayama, K Fujiwara, K Ueno, T Shimada, K Saiki

      JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS42 ( 12A ) L1408 - L1410   2003年12月

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      記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:INST PURE APPLIED PHYSICS  

      We present a simple but powerful method to determine the thicknesses of the accumulation and depletion layers and the distribution curve of injected carriers in organic field effect transistors. The conductivity of organic semiconductors in thin film transistors was measured in situ and continuously with a bottom contact configuration, as a function of film thickness at various gate voltages. Using this method, the thicknesses of the accumulation and depletion layers of pentacene were determined to be 0.9 nm (V-G = - 15 V) and 5 nm (V-G = 15 V), respectively.

      DOI: 10.1143/JJAP.42.L1408

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    MISC

    • Fe-Sn薄膜素子が示す異常ホール効果と磁気抵抗効果を用いた磁気センサ応用

      塩貝 純一, 藤原 宏平, 塚﨑 敦

      日本磁気学会第244回研究会資料244-4   121 - 25   2023年9月

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    • トポロジカル物質を用いた薄膜磁気センサ 招待有り 査読有り

      藤原 宏平, 塩貝 純一, 塚﨑 敦

      応用物理92 ( 1 ) 20 - 24   2023年1月

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      担当区分:筆頭著者   記述言語:日本語   掲載種別:記事・総説・解説・論説等(学術雑誌)  

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    • パリレンゲート絶縁膜を用いた機能性酸化物のトランジスタ動作と電界物性制御

      藤原 宏平

      高分子絶縁材料の絶縁破壊・劣化メカニズムとその対策技術   291 - 298   2021年1月

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      担当区分:筆頭著者, 責任著者   掲載種別:記事・総説・解説・論説等(商業誌、新聞、ウェブメディア)  

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    • Fe-Sn 合金薄膜の異常ホール効果を用いた磁場センサ 招待有り

      藤原 宏平, 塚﨑 敦

      日本磁気学会第226回研究会資料226-4 ( 19 )   2020年1月

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      記述言語:日本語  

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    • ポリマーゲート絶縁膜を用いた酸化物トランジスタの作製 査読有り

      藤原 宏平

      電気学会論文誌C139   207 - 210   2019年3月

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      記述言語:日本語   掲載種別:記事・総説・解説・論説等(学術雑誌)  

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    • セレン化鉄および関連化合物の薄膜作製と物性評価 招待有り

      藤原 宏平, 塩貝 純一, 塚﨑 敦

      応用物理学会結晶工学分科会第148回研究会   21 - 25   2018年4月

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      記述言語:日本語   掲載種別:記事・総説・解説・論説等(学術雑誌)  

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    • ポリパラキシリレン薄膜の形成と酸化物電界効果素子への応用

      藤原 宏平, 大内 誠, 山内 秀彦

      電気学会電子材料研究会資料EDM-17-025   13 - 16   2017年11月

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      記述言語:日本語   掲載種別:記事・総説・解説・論説等(学術雑誌)  

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    講演・口頭発表等

    • コランダム類縁構造酸化物の薄膜物質開発と物性評価 招待有り

      藤原 宏平, 塚﨑 敦

      第83回応用物理学会秋季学術講演会  2022年9月22日 

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      記述言語:日本語  

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    • Topological Hall effect in multilayers of kagome-lattice ferromagnet Fe3Sn and Pt 招待有り

      藤原 宏平

      Indo-Japan Workshop on Interface Phenomena for Spintronics  2022年3月9日 

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    • 新奇デバイス機能の実現に向けた金属酸化物の薄膜化研究 招待有り

      藤原 宏平

      2021年日本表面真空学会学術講演  2021年11月3日 

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    • ポリマー/酸化物界面における電気伝導制御とトランジスタ機能 招待有り

      藤原 宏平

      令和3年電気学会全国大会シンポジウムS8「無機薄膜のフレキシブルコーティングおよび異種材料接合技術」  2021年3月10日 

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      会議種別:口頭発表(招待・特別)  

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    • 極性構造・異常原子価・ハニカム格子に着目した酸化物薄膜研究 招待有り

      藤原 宏平

      酸化物研究の新機軸に向けた学際討論会  2021年3月2日 

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    • Fe-Sn合金薄膜の異常ホール効果を用いた磁場センサ 招待有り

      藤原 宏平

      日本磁気学会第226回研究会/第74回スピントロニクス専門研究会  2020年1月17日 

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      会議種別:口頭発表(招待・特別)  

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    • Thin-film growth and interface engineering of high-mobility Sn oxides 招待有り

      藤原 宏平

      Dept. Phys. Seminar, University of Seoul  2019年10月30日 

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    • New aspects of Sn-based transparent conducting oxides: high-mobility interface and its potential coupling with spontaneous polarization 招待有り

      藤原 宏平

      KIST-KINKEN symposium 2019, Korea Institute of Science and Technology  2019年10月29日 

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    • 高移動度スズ系酸化物の薄膜合成と界面伝導評価 招待有り

      藤原 宏平

      日本放射光学会第11回若手研究会「放射光を用いたナノ分光技術とスピントロニクスとの協奏」  2019年8月 

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      記述言語:日本語   会議種別:口頭発表(招待・特別)  

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    • Field-effect transistor based on crystalline ZnSnO3 grown by molecular beam epitaxy 招待有り 国際会議

      藤原 宏平

      4th EMRS & MRS-J Bilateral Symposium on Advanced Oxides and Wide Bandgap Semiconductors  2018年10月 

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      記述言語:英語   会議種別:口頭発表(招待・特別)  

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    • 薄膜合成と界面制御による酸化物トランジスタの機能向上 招待有り

      藤原 宏平

      日本セラミックス協会第31回秋季シンポジウム  2018年9月 

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      記述言語:日本語   会議種別:口頭発表(招待・特別)  

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    • 薄膜化学で切り拓く酸化物トランジスタの新機能 招待有り

      藤原 宏平

      電子情報通信学会信越支部講演会  2018年6月 

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      記述言語:日本語   会議種別:口頭発表(招待・特別)  

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    • セレン化鉄および関連化合物の薄膜作製と物性評価 招待有り

      藤原 宏平

      応用物理学会第148回結晶工学分科会研究会  2018年4月 

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      記述言語:日本語   会議種別:口頭発表(招待・特別)  

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    • 静電キャリアドーピングによるBaSnO3薄膜の電子移動度向上 招待有り

      藤原 宏平

      第27回日本MRS年次大会  2017年12月 

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      記述言語:日本語   会議種別:口頭発表(招待・特別)  

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    • ポリパラキシリレン薄膜の形成と酸化物電界効果素子への応用 招待有り

      藤原 宏平, 大内 誠, 山内 秀彦

      電子材料研究会フレキシブルセラミックスコーティング研究会  2017年11月23日 

      詳細を見る

    • ポスト遷移金属の酸化物を用いた薄膜素子研究 招待有り

      藤原 宏平

      ポスト新機能物質開発のための戦略会議  2017年11月15日 

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    • スズ系複酸化物のエピタキシャル成長と電子機能開拓 招待有り

      藤原 宏平

      第64回応用物理学会春季学術講演会  2017年3月 

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      記述言語:日本語   会議種別:口頭発表(招待・特別)  

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    • Dual field effects in spinel ferrite electric-double layer transistors: electrostatic carrier doping and redox reactions 招待有り 国際会議

      藤原 宏平

      14th International Union of Materials Research Societies-International Conference on Advanced Materials  2015年10月 

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      記述言語:英語   会議種別:口頭発表(招待・特別)  

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    • 機能性酸化物PLD技術 招待有り

      藤原 宏平

      文部科学省ナノテクノロジープラットフォーム平成26年度セミナー成膜プロセス技術実践セミナー  2015年2月18日 

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    • Growth of Complex Nanostructures of Metal Oxides Using a Shadow Effect 招待有り 国際会議

      藤原 宏平

      International Union of Materials Research Society–International Conference on Electronic Materials  2014年6月 

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      記述言語:英語   会議種別:口頭発表(招待・特別)  

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    • Tuning the Transport Properties of Ferrite Thin Films by Electric-Double-Layer Gating 招待有り 国際会議

      藤原 宏平

      23rd Annual Meeting of MRS-Japan, International Symposium  2013年12月 

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      記述言語:英語   会議種別:口頭発表(招待・特別)  

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    • 陰影効果を利用した金属酸化物ナノ構造の局所成長 招待有り

      藤原 宏平, 岡田 浩一, 服部 梓, 田中 秀和

      附置研究所間アライアンスによるナノとマクロをつなぐ物質・デバイス・システム創製戦略プロジェクト第1回アライアンス若手研究交流会  2013年11月26日 

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    • 遷移金属ナノ構造の酸化還元を利用した抵抗変化デバイス 招待有り

      藤原 宏平

      第74回応用物理学会秋季学術講演会  2013年9月 

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      記述言語:日本語   会議種別:口頭発表(招待・特別)  

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    • Electric-Field-Induced Phase Transition in Charge-Ordered LuFe2O4 Thin Films 招待有り

      K. Fujiwara, T. Hori, H. Tanaka

      21th International Conference on Composites/Nano Engineering  2013年7月23日 

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    • Observation of Local Electrochemical Phase Change in Resistive Switching Devices 招待有り

      K. Fujiwara, Y. Konno, Y. Nakamura, M. J. Rozenberg, H. Takagi

      19th International Conference on Composites/Nano-Engineering  2011年7月25日 

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    • Resistance Switching and Formation of a Conductive Bridge in Metal/Binary Oxide/Metal Structure for Memory Devices 招待有り

      藤原 宏平

      第71回応用物理学会学術講演会  2010年9月 

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      記述言語:日本語   会議種別:口頭発表(招待・特別)  

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    • 遷移金属酸化物抵抗変化メモリーにおける局所相変化機構 招待有り

      藤原 宏平

      日本放射光学会第二回若手研究会「顕微分光のフロンティア」  2010年8月 

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      記述言語:日本語   会議種別:口頭発表(招待・特別)  

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    共同研究・競争的資金等の研究

    • トポロジカル物質群のアモルファス薄膜材料化

      科学技術振興機構  創発的研究支援事業 

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      2023年4月 - 2026年3月

      担当区分:研究代表者 

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    • 極薄膜のトポタクティック反応によるカゴメ格子単層物質の創製と量子機能物性の実証

      日本学術振興会  学研究費補助金・基盤研究(B) 

      藤原宏平

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      2023年4月 - 2026年3月

      課題番号:23H01830

      担当区分:研究代表者 

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    • 薄膜安定化した極性酸化物半導体におけるマルチレベル強誘電メモリ機能の実証

      日本学術振興会  科学研究費補助金・基盤研究(B) 

      藤原 宏平

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      2019年4月 - 2021年3月

      担当区分:研究代表者  資金種別:競争的資金

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    • ゲート電界による鉄酸化物薄膜の酸化状態制御と相変化デバイス機能の開拓

      日本学術振興会  科学研究費補助金・基盤研究(B) 

      藤原 宏平

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      2015年4月 - 2018年3月

      担当区分:研究代表者  資金種別:競争的資金

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    • スピン流計の実現

      日本学術振興会  科学研究費補助金・挑戦的萌芽研究 

      藤原 宏平

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      2015年4月 - 2017年3月

      担当区分:研究代表者  資金種別:競争的資金

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    • 鉄系酸化物の室温電子固体状態における電子相変化機能の実証

      日本学術振興会  科学研究費補助金・若手研究(B) 

      藤原 宏平

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      2013年4月 - 2015年3月

      担当区分:研究代表者  資金種別:競争的資金

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    • 二元系遷移金属酸化物における電界誘起抵抗変化現象の機構解明

      日本学術振興会  科学研究費補助金・若手研究(B) 

      藤原 宏平

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      2010年4月 - 2013年3月

      課題番号:22760519

      担当区分:研究代表者  資金種別:競争的資金

      遷移金属酸化物で発現する抵抗スイッチング現象のメカニズム解明、特に酸化還元反応の関与を実験的に明らかにすることを目指した。デバイス内部の局所領域で発現するとされる化学変化を検出するためのユニークなデバイス構造として、抵抗変化サイトが予め規定されたナノワイヤー型素子を開発した。 Ni ナノワイヤー素子を用いた三次元ナノ光電子分光実験から、 抵抗スイッチングに伴い NiO への酸化 (高抵抗化) ・金属 Ni への再還元 (低抵抗化)が生じることを見出し、抵抗スイッチングの微視的起源が酸化還元であることを実証することに成功した。

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    • スピンホール効果を用いた5d電子系酸化物におけるスピン・軌道相互作用の学理構築

      日本学術振興会  科学研究費助成事業 

      松野 丈夫, 福間 康裕, 藤原 宏平

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      2010年 - 2012年

      課題番号:22340108

      担当区分:研究分担者 

      配分額:19370000円 ( 直接経費:14900000円 、 間接経費:4470000円 )

      5d 遷移金属酸化物IrO_2 の逆スピンホール効果を検出し,スピン流→電圧変換の性能指数であるスピンホール抵抗率がPt の10 倍程度となることを示した.5d 遷移金属酸化物においてスピン・軌道相互作用が支配的であることを輸送現象から初めて見出すとともに,高効率スピン流検出用材料としての可能性を証明した.また,SrIrO_3 とSrTiO_3 からなる人工超格子が新たなモット絶縁体であることを見出し,スピン・軌道相互作用と電子相関の協奏に及ぼす次元性の効果を明らかにした.

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    • 強相関ヘテロ接合の創成—学理解明とデバイス応用

      日本学術振興会  科学研究費補助金・特別研究員奨励費DC1 

      藤原 宏平

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      2005年4月 - 2008年3月

      課題番号:05J11868

      担当区分:研究代表者  資金種別:競争的資金

      金属/遷移金属酸化物/金属サンドイッチ構造における抵抗スイッチング効果に関する研究 遷移金属酸化物が示す抵抗スイッチング効果が大きな注目を集め,活発に研究されている.その動機は二つあり,次世代不揮発性メモリである抵抗メモリ素子への応用及び現象の物理的起源の解明である.著者はこれまでに,CuOにおける抵抗スイッチング効果の舞台が,ソフト絶縁破壊操作によって酸化物中に形成される導電性パスであることを明らかにしてきた.本年度は以下の実験を行った.
      1,導電性パスの形成位置及びサイズの制御
      パスの形成は一種の絶縁破壊であることが昨年度までの結果から明らかになっているため,局所的な電界集中領域を電極パターンに導入することで,パスの形成位置制御を試みた.形成されたパスは電界集中領域にピン止めされるとともに,電極間距離の調整によって,パスサイズを減少させることも出来ることが分かった.また,それに伴って,スイッチング電圧・電流が大幅に低減されることも分かった.即ち,当該効果は将来の素子微細化・高集積化の中でも高いポテンシャルを有する.
      2,導電性パスの化学分析
      導電性パスは酸化物が溶融しな外観を持つ.抵抗スイッチング動作の低抵抗状態では,素子は金属伝導を示すため,母体酸化物の還元による金属の形成が期待される.この推測に基づいて,光電子顕微鏡・エネルギー分散型X線分析などによる化学組成の評価(Cuの価数分析・定性定量分析)を行った結果,パス構造は強く還元されたCuOから成ることが明らかになり,また金属Cuの存在も強く示唆された.化学状態は空間的に不均ーであることから,一種の非平衡的な反応の関与が推察される.
      2,導電性パスの化学分析
      導電性パスは酸化物が溶融しな外観を持つ.抵抗スイッチング動作の低抵抗状態では,素子は金属伝導を示すため,母体酸化物の還元による金属の形成が期待される.この推測に基づいて,光電子顕微鏡・エネルギー分散型X線分析などによる化学組成の評価(Cuの価数分析・定性定量分析)を行った結果,パス構造は強く還元されたCuOから成ることが明らかになり,また金属Cuの存在も強く示唆された.化学状態は空間的に不均ーであることから,一種の非平衡的な反応の関与が推察される.

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    産業財産権

    • 層状半導体、層状半導体の製造方法

      塚﨑 敦, 寺田 吏, 藤原 宏平

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      出願人:国立大学法人東北大学

      出願番号:特願2024-175672  出願日:2024年10月7日

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    • 熱電変換装置

      塚﨑 敦, 藤原 宏平, 塩貝 純一

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      出願人:東北大学

      出願番号:特願PCT/JP2022/038027  出願日:2022年10月12日

      公開番号:特開WO 2024/079811 A1  公開日:2024年4月18日

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    • ホール素子

      塚﨑 敦, 藤原 宏平

      詳細を見る

      出願番号:特願2018-157542  出願日:2018年8月24日

      公開番号:特開WO 2020/040264  公開日:2020年2月27日

      特許番号/登録番号:特許第7461651  登録日:2024年3月27日 

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    • 薄膜及びその製造方法、熱電変換素子、磁気抵抗効果素子、磁気メモリ並びに磁気センサ

      塚﨑 敦, 藤原 宏平, 須﨑 友文, 水野 弘樹, 深堀 明博

      詳細を見る

      出願人:東北大学、三菱ケミカル

      出願番号:特願2022-058190  出願日:2022年3月31日

      公開番号:特開2023-149556  公開日:2023年10月13日

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    • 磁気素子

      金澤 直也, 大塚 悠介, 堀 智洋, 平山 元昭, 十倉 好紀, 塚﨑 敦, 藤原 宏平

      詳細を見る

      出願人:東京大学、東北大学

      出願番号:特願2022-030135  出願日:2022年2月28日

      公開番号:特開2023-126707  公開日:2023年9月8日

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    • 横熱電変換材料、横熱電変換素子及び熱電変換モジュール

      塚﨑 敦, 藤原 宏平, 水野 弘樹, 須﨑 友文

      詳細を見る

      出願人:東北大学、三菱ケミカル株式会社

      出願番号:特願2023-047069  出願日:2023年3月23日

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    • 磁気センサおよび磁気検出方法

      塚﨑 敦, 藤原 宏平, 塩貝 純一

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      出願人:東北大学

      出願番号:特願PCT/JP2022/6778  出願日:2022年2月18日

      特許番号/登録番号:特許第7244157  登録日:2023年3月13日 

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    • 電流-スピン流変換素子

      藤原 宏平, 福間 康裕, 松野 丈夫, 大谷 義近, 髙木 英典

      詳細を見る

      出願人:独立行政法人理化学研究所

      出願番号:特願2010-191414  出願日:2010年8月27日

      公開番号:特開2012-049403  公開日:2012年3月8日

      特許番号/登録番号:特許第5590488号  発行日:2014年8月8日

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    • サーミスタ素子

      髙木 英典, 中村 吉伸, 藤原 宏平

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      出願人:株式会社東京大学TLO、エヌイーシーショットコンポーネンツ株式会社

      出願番号:特願2004-079818  出願日:2004年3月19日

      公開番号:特開2005-268578  公開日:2005年9月29日

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