鹿児島大学 · 理工学研究科 · 教授

研究キーワードHeusler alloys・spintronics・antiferromagnetic resonance・high magnetic field physics・magnetic phase diagrams・thermal analysis・superconductor junctions

研究分野構造・機能材料・固体物性Ⅱ(磁性・金属・低温)・工学・材料工学・物理学・理学・理工系・金属物性

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• Mitsui Y., Fumoto S., Kobayashi R., Takahashi K., Koyama K. . High Magnetic Field Effects on Phase Transformation Kinetics of ε-Mn-Al Probed Using Differential Thermal Analysis . MATER2024 · 担当区分： 最終著者 記述言語： 英語 掲載種別： 研究論文（学術雑誌） 出版者・発行元： 公益社団法人 日本金属学会 Differential thermal analysis (DTA) on quenched Mn55Al45 with hcp structure (ε-phase) was performed under magnetic fields up to 15 T in order to investigate the magnetic field effects on the transformation kinetics of ε-phase. So far, the annealing of ε-phase under magnetic field indicated the acceleration of the phase transformation from the ε-phase to the metastable ferromagnetic τ-phase with L10 structure and the suppression of the decomposition into the equilibrium phase (β-phase). In this study, as the magnetic field intensity increased, the transformation temperature from ε-phase gradually decreased to the lowest value in the range from 0 to 4 T. A single exothermic peak was observed on each DTA curve, and it was found that the peak contained plural exothermic ε–τ and τ–β transformations. Activation energy of the transformation also showed the lowest value in the magnetic field range from 4 to 10 T, suggesting that the activation energy of the ε–τ transformation decreases at low magnetic field region from 0 to 4 T and the activation energy of the τ–β transformation increases at high magnetic field region from 10 to 15 T. These changes in activation energy were discussed by contribution of Zeeman energy for nucleation of the τ-phase in the ε-matrix and that of β-phase from the τ-phase. [doi:10.2320/matertrans.MT-M2024129] DOI： 10.2320/matertrans.mt-m2024129 Scopus CiNii Research
• クレーンゲームで学ぶ物理学2024 · 集英社インターナショナル 2024年 （ ISBN: 9784797681390 ）
• Sueyoshi Y., Kobayashi R., Onoue M., Mitsui Y., Umetsu R.Y., Koyama K. . Structural and Magnetic Properties of MnCo1-xFexGe1-y2024 · 記述言語： 英語 出版者・発行元： 公益社団法人 日本金属学会 Magnetic and structural properties of MnCo<inf>1−x</inf>FexGe<inf>1−y</inf>Siy (x, y = 0, 0.5) were investigated using X-ray powder diffraction and magnetization measurements in the temperature (T) range from 5 to 370 K and in magnetic fields up to μ<inf>0</inf>H = 5 T. At room temperature, MnCoGe and MnCoGe<inf>0.5</inf>Si<inf>0.5</inf> were the orthorhombic crystal structure (M-phase), MnCo<inf>0.5</inf>Fe<inf>0.5</inf>Ge was the hexagonal crystal structure (P-phase), and MnCo0.5Fe0.5Ge0.5Si0.5 had two-phase coexistence of the M- and P-phases. MnCoGe and MnCo<inf>0.5</inf>Fe<inf>0.5</inf>Ge were a simple ferromagnetic and their Curie temperatures (TC) were determined to be 340 K and 200 K, respectively. MnCoGe<inf>0.5</inf>Si<inf>0.5</inf> and MnCo<inf>0.5</inf>Fe<inf>0.5</inf>Ge<inf>0.5</inf>Si<inf>0.5</inf> in μ0H ≤ 1 T showed a gentle dip in thermomagnetic curves at 10 ≤ T ≤ 100 K below TC which disappears when a magnetic field of μ0H > 3 T was applied. The magnetization curves of MnCoGe<inf>0.5</inf>Si<inf>0.5</inf> and MnCo<inf>0.5</inf>Fe<inf>0.5</inf>Ge<inf>0.5</inf>Si<inf>0.5</inf> at 5 K exhibited that a metamagnetic transition with the magnetic hysteresis in 0 < μ<inf>0</inf>H < 3 T. Our results suggest that substituting Fe for Co in MnCoGe system weakens the ferromagnetic interaction, whereas substituting Si for Ge strengthens the antiferromagnetic interaction. DOI： 10.2320/matertrans.mt-mbw2024001 Scopus CiNii Research
• Kobayashi R., Mitsui Y., Yoshizaki Y., Takahashi K., Takamine K., Koyama K. . Controlling the growth of yeast by culturing in high magnetic fields . Journal of Magnetism and Magnetic M2023 · 記述言語： 英語 掲載種別： 研究論文（学術雑誌） 出版者・発行元： Journal of Magnetism and Magnetic Materials The effect of static magnetic fields up to a strength of 15 T on the growth of three types of yeast which were all classified as Saccharomyces cerevisiae was studied. The growth rate of the yeasts was suppressed by applying a magnetic field. The degree of suppression depended on the type of yeast. The reduction in the numbers of yeast cells was due to growth suppression, not sterilization. Among the three types of Saccharomyces cerevisiae, the degree of suppression on the growth of two yeasts was strongest in a magnetic field at 8 T with different suppression degree of 19% and 12% for a culture time of 24 h. Growth of the other yeast most suppressed by 10% at a magnetic field of around 4 T. Therefore, the yeasts have their characteristic magnetic field sensitivity on the growth. The results were discussed using a model based on the competition between yeast osmotic pressure changes by magnetic field and magnetic forces induced by magnetic field gradient. In low magnetic field regions, change of the osmotic pressure shrink the yeast cell and reduce the contact frequency between yeast cells and glucose-based ions. In higher magnetic field regions, effect of magnetic force become apparent, and recover the growth rate of the yeast. It suggested that the selective growth of yeast can be expected by in-magnetic-field culturing. DOI： 10.1016/j.jmmm.2023.171193 Scopus

• 多種・多数の磁性相を含む２元合金系の磁場中状態図と磁場中合成過程の解明2023 · 配分額： 18980000円 （ 直接経費： 14600000円 、 間接経費： 4380000円 ）
• 鉄基強磁性材料中の原子拡散における磁場抑制効果の解明2022 · 担当区分： 研究代表者
• 強磁場中平衡状態図に基づいた元素磁気分離法への挑戦2021 · 配分額： 6370000円 （ 直接経費： 4900000円 、 間接経費： 1470000円 ）
• ひらめき☆ときめきサイエンス～ようこそ大学の研究室へ～KAKENHI 研究成果の社会還元・普及事業2020 · 日本学術振興会 鹿児島大学理学部101教室 2020年10月

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