Kagoshima University · Cooperative Division, Integrated Science Domain · 講師

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• 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 researchmap
• Takahashi J., Mitsui Y., Onoue M., Kobayashi R., Koyama K. . Nitridation kinetics of Sm2Fe17 probed using Mössbauer spectroscopy . Journal of Magnetism and Magnet2022 · 記述言語： 日本語 掲載種別： 研究論文（学術雑誌） 出版者・発行元： Journal of Magnetism and Magnetic Materials In this study, the Sm2Fe17 powder was subjected to nitridation at 743 K under N2 pressures of 0.05 and 0.1 MPa to investigate the growth kinetics of Sm–Fe–N. Two-phase growth of the fully nitride (FN) Sm2Fe17N3 phase and the nitrogen-poor (NP) Sm2Fe17Nx phase (0 < x < 3; x denotes the nitrogen content) was observed using 57Fe Mössbauer spectroscopy. Although the x value was greater at 0.05 MPa than at 0.1 MPa in the early stage of nitridation, the opposite trend was observed in the later stage. At a nitrogenation time of 24 h, nitridation was nearly complete at 0.1 MPa, while x tended to saturate and did not reach 3 at 0.05 MPa. The nitridation process was discussed based on two simultaneous growth processes: (i) the diffusion of the nitrogen atom in the NP phase and (ii) the nucleation and growth of the FN phase. A process combining N2 pressure and nitrogenation, which facilitated nitrogenation under low N2 pressure and high N2 pressure at the beginning and end of the nitridation process, respectively, achieved faster nitridation than process with a single N2 pressure. DOI： 10.1016/j.jmmm.2022.169295 Scopus researchmap
• Onaka A., Onoue M., Onodera R., Mitsui Y., Koyama K. . Magnetic and structural properties of Fe-substituted MnCoGe with Ni2In-type structure . Journal of Magnetism and Magne2022 · 記述言語： 日本語 掲載種別： 研究論文（学術雑誌） 出版者・発行元： Journal of Magnetism and Magnetic Materials Site occupation of Fe atoms, magnetic and structural properties in MnCo1-xFexGe (x = 0.2, 0.5, 0.7 and 1.0) were investigated. Two phase co-existence of the hexagonal Ni2In-type structure (P-phase) and the orthorhombic TiNiSi-type structure was observed at room temperature for x = 0.2. For x = 0.5, 0.7 and 1.0, MnCo1-xFexGe was confirmed to be the P-phase. With increasing x from 0.2 to 1.0 for the P-phase, the lattice parameter ap slightly increased by only 0.14%, but cp decreased by 2.1%. As a result, when x was increased from 0.2 to 1.0, the unit cell volume of the P-phase decreased monotonously by 1.8%. The saturation magnetic moment and Curie temperature of MnCo0.5Fe0.5Ge were 2.16 μB/f.u. and 205 K, respectively, which decreased monotonically with increasing x. 57Fe Mössbauer spectroscopy indicated that 90–94% of the substituted Fe atoms occupied the Co-site but 10–6% of the Fe also occupied the Mn-site in the P-phase. For x = 0.5, 0.7 and 1.0, the hyperfine field at the Co-site was 8.29–9.44 T, which was larger than that at the Mn-site. The sign of quadruple splitting at the Co-sites changed from positive to negative with the increase of x, suggesting that the electric field gradients at Co-sites changed. DOI： 10.1016/j.jmmm.2022.170000 Scopus researchmap
• Mitsui Y., Onoue M., Kobayashi R., Sato K., Kuzuhara S., Ito W., Takahashi K., Koyama K. . High Magnetic Field Effects on Cu-precipitation Behavior of Fe-1mass%Cu at 773 K . ＩＳＩＪ Ｉｎｔｅｒ2021 · 記述言語： 英語 掲載種別： 研究論文（学術雑誌） 出版者・発行元： 一般社団法人 日本鉄鋼協会 Tramp elements in steel, such as Cu and Sn, cannot be removed by acid treatment. Since these elements condense by repeating recycling process, leading to deterioration of strength. Therefore, the methods for avoiding condensation or removing tramp elements are required. In this study, in-magnetic-field annealing process was focused on because magnetic field is effective for diffusion, phase transformation, phase diagram and precipitation. In-magnetic-field annealing of Fe-1mass%Cu at 773 K was performed in 5 and 10 T for investigating precipitation behavior of supersaturated Cu. From microstructural observation, precipitation of Cu-rich phase in Fe-matrix, and magnetic field effect on itself were not observed clearly. Increase of the hyperfine field was detected for the samples annealed at 5 T by Mössbauer spectroscopy, indicating the enhancement of the Cu-precipitation. On the contrary, hyperfine field for 10T-annealed sample was slightly smaller than that for 0 T. Therefore, in-field annealing effect on Cu-precipitation became unclear at 10 T. These magnetic field effects were discussed in the viewpoints of the change of Cu–Fe phase diagram and the atomic diffusion under magnetic field. Difference of the magnetic field effects on precipitation between 5 T and 10 T is explained by the competition between the enhancement of the driving force of the precipitation and suppression of the atomic diffusion. The obtained results indicated that there is optimized magnetic field intensity for controlling Cu-precipitation. DOI： 10.2355/isijinternational.isijint-2021-404 Scopus CiNii Research researchmap

• Fe-57メスバウア分光測定による鉄置換3d遷移金属化合物の機能性発現機構の解明2023 · 担当区分： 研究代表者 資金種別： 競争的資金 配分額： 4680000円 （ 直接経費： 3600000円 、 間接経費： 1080000円 ） researchmap

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