研究等業績 - 原著論文 - 吉村 哲
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B. Dash, K. L. Routray, S. Saha, S. Yoshimura, S. Ratha, M. K. Rout
Transactions on Electrical and Electronic Materials ( Transactions on Electrical and Electronic Materials ) 25 ( 2 ) 232 - 246 2024年03月 [査読有り]
研究論文（学術雑誌） 国際共著
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Sunirmal Saha, Krutika Routray, Pritish. Hota, Biswajita Dash, Satoru Yoshimura, Soumyaranjan Ratha, and Traibhab Kumar Nayak
Journal of Molecular Structure ( Journal of Molecular Structure ) 1302 2024年03月 [査読有り]
研究論文（学術雑誌） 国際共著
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S. Ratha, G. Egawa, S. Yoshimura
Applied Surface Science ( Applied Surface Science ) 643 158704 2024年01月 [査読有り]
研究論文（学術雑誌） 国内共著
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α”-Fe<sub>16</sub>N<sub>2</sub>薄膜の高密度磁気記録媒体への応用に向けた反応性パルスDCスパッタリング成膜条件の検討および結晶化促進
勝山 郁子, 江川 元太, 吉村 哲
日本素材物性学会誌 ( 日本素材物性学会 ) 34 ( 0 ) 6 - 14 2024年01月 [査読有り]
研究論文（学術雑誌） 国内共著
<p>An α"-Fe<sub>16</sub>N<sub>2</sub> has very high magnetic crystalline anisotropy energy even if magnetic anisotropy field is not so large because of its very high saturation magnetization. Therefore, magnetization switching field of this material is smaller than that of L1<sub>0</sub>-FePt which has very high magnetic crystalline anisotropy energy due to having very high magnetic anisotropy field. As the results, α"-Fe<sub>16</sub>N<sub>2</sub> seems one of the suitable materials for next-generation high density magnetic recording media without energy assisted recording system. In this study, for fabrication of α"-Fe<sub>16</sub>N<sub>2</sub> thin fi lms, we newly attempted a pulsed DC（P-DC） reactive sputtering method, which is expected to provide high quality in the formation of oxide/nitride thin films with complex crystal structures. Since there have been no attempts to fabricate this thin fi lms with this method before, we investigated the influence of film properties （composition） on deposition parameters such as pulse frequency, deposition power, and target-substrate （T-S） distance, and fi nally optimized the deposition conditions to obtain the nitrogen concentration of Fe:N ＝ 16:2 in the film. As a result, with decreasing pulse frequency, with increasing deposition power, and with decreasing T-S distance, nitrogen concentration in the thin fi lm decreased, and it was clear that the optimized deposition conditions to obtain the nitrogen concentration of Fe:N ＝ 16:2 in the thin fi lm were pulse frequency: 25 kHz, deposition power: 200 W, and T-S distance: 100 mm, respectively. Using these deposition conditions, we investigated the deposition temperature and VHF plasma irradiation power to promote the α" phase formation and crystallization in the fabrication of Fe-N thin films on MgO（100） single crystalline substrates. As a result, it was found that α" phase formation and crystallization were most enhanced at a deposition temperature of 200 ℃ and a VHF plasma irradiation power of 3 W （<i>V</i><sub>dc</sub>: -18 to -16 V）. The usefulness of P-DC power source for fabrication of α"-Fe<sub>16</sub>N<sub>2</sub> thin fi lms was confi rmed by comparing to Fe-N thin fi lms fabricated by using a DC power source. As a result, reactive P-DC sputtering method was found to have a positive impact on α" phase formation and crystallization.</p>
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Biswajita Dash, Sunirmal Saha, Satoru Yoshimura, Soumyaranjan Ratha, and Jashashree Ray
Journal of Materials Science: Materials in Electronics ( Journal of Materials Science: Materials in Electronics ) 34 ( 36 ) 2023年12月 [査読有り]
研究論文（学術雑誌） 国際共著
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Satoru Yoshimura, Naoya Oshita, Genta Egawa, and Munusamy Kuppan
Nanotechnology ( Nanotechnology ) 34 ( 46 ) 465703 2023年08月 [査読有り] [招待有り]
研究論文（学術雑誌） 国内共著
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M. Mottakin, V. Selvanathan, Md. A. Islam, H. Almohamadi, N. H. Alharthi, S. Yoshimura, Md. Akhtaruzzaman
Chemistry - An Asian Journal ( Chemistry - An Asian Journal ) e202300532 2023年08月 [査読有り]
研究論文（学術雑誌） 国際共著
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Soumyaranjan Ratha, Munusamy Kuppan, Genta Egawa, Satoru Yoshimura
Nano-Structures & Nano-Objects ( Elsevier ) 35 101007 2023年07月 [査読有り]
研究論文（学術雑誌） 国内共著
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M. Mottakin, Vidhya Selvanathan, Syaza Amira Razali, Md. Ariful Islam, Hamad Almohamadi, Nabeel H. Alharthi, Satoru Yoshimura, Md. Akhtaruzzaman
Electrochimica Acta ( Elsevier ) 463 142861 2023年07月 [査読有り]
研究論文（学術雑誌） 国際共著
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強磁性・強誘電(Bi,La)(Fe1-yMy)O3(M=Ni,Co)薄膜の磁気特性に及ぼすBサイトの置換元素および置換量の効果
鈴木 悠太, 尾関 拓海, 江川 元太, 吉村 哲
日本素材物性学会誌 ( 日本素材物性学会 ) 33 ( 1_2 ) 12 - 17 2023年04月 [査読有り]
研究論文（学術雑誌） 国内共著
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S. Ratha, D. Yamamoto, K. Takeda, M. Kuppan, G. Egawa, and S. Yoshimura
International Journal of the Society of Materials Engineering for Resources ( 日本素材物性学会 ) 25 ( 2 ) 174 - 178 2022年10月 [査読有り]
研究論文（学術雑誌） 国内共著
<p>(Bi<sub>0.5</sub><i>L</i><sub>0.5</sub>)(Fe<sub>0.7</sub>Co<sub>0.3</sub>)O<sub>3</sub> (<i>L </i>=<i> </i>La, Nd, Sm, Gd, Dy) thin films with ferromagnetism and ferroelectricity were fabricated using pulsed DC sputtering technique to obtain high saturation magnetization, perpendicular magnetic anisotropy and large magnetic Kerr effect. These magnetic properties are very important for realization of high performance magnetic devices driven by electric field. All (Bi<sub>0.5</sub><i>L</i><sub>0.5</sub>)(Fe<sub>0.7</sub>Co<sub>0.3</sub>)O<sub>3</sub> (<i>L </i>=<i> </i>La, Nd, Sm, Gd, Dy) thin films had relatively high saturation magnetization, perpendicular magnetic anisotropy and magnetic Kerr effect. Especially, (Bi<sub>0.5</sub>Nd<sub>0.5</sub>)(Fe<sub>0.7</sub>Co<sub>0.3</sub>)O<sub>3</sub> thin film had a very high saturation magnetization of 140 emu/cm<sup>3</sup> (1.40×10<sup>5</sup> A/m), a high perpendicular magnetic anisotropy of 2.6 at ratio of perpendicular coercivity against in-plane coercivity and (Bi<sub>0.5</sub>La<sub>0.5</sub>)(Fe<sub>0.7</sub>Co<sub>0.3</sub>)O<sub>3</sub> thin film had a very high magnetic Kerr rotation angle of 0.72°. These magnetic properties were excellent compared with the case of (Bi<sub>0.5</sub><i>A</i><sub>0.5</sub>)FeO<sub>3</sub> (<i>A </i>=<i> </i>Ca, Sr, Ba) thin films with the maximum value of 90 emu/cm<sup>3</sup> (9.0×10<sup>4</sup> A/m) (for saturation magnetization), 0.8 (for ratio of Perpendicular coercivity against in-plane coercivity) and 0.03° (for magnetic Kerr rotation angle) which were fabricated previously. These magnetic properties are very important for realization of high performance magnetic devices driven by electric field.</p>
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Investigations on Spintronic RFeO₃ Crystals Grown by Optical Floating Zone Technique
P. Ramesh Babu, S. Kalainathan, and S. Yoshimura
International Journal of the Society of Materials Engineering for Resources ( 日本素材物性学会 ) 25 ( 2 ) 179 - 182 2022年10月 [査読有り] [招待有り]
研究論文（学術雑誌） 国際共著
<p>Magnetic crystals are physically important to know their intrinsic magnetic properties. Magnetic crystals are also technologically important and their creation has aided crystal growth significantly. Rareearth orthoferrites material (RFeO<sub>3</sub>) is one of the major components used in manufacturing sophisticated gadgets. This study focuses on the growth and physical properties of the optically generated RFeO<sub>3</sub> (R=Y, Gd and Sm) single crystals. The floating zone method generates single crystals of 3-20 mm/h in the optical zone. The purity of the grown materials was confirmed from the Powder X-Ray Diffraction (PXRD) analysis. The addition of Gd to YFeO<sub>3</sub> increases the lattice parameters of the material. Magnetic properties of the grown crystal were studied between 20-700 K. At high temperature, two anomalous effects were observed, one at (T<sub>SR</sub>=480 K) due to spin reorientation and the other is antiferromagnetic (AFM) to paramagnetic transitions at (T<sub>N</sub>= 670 K). Bloch parameter was also calculated. Microhardness value decreases nonlinearly. When the applied load is greater than 1.96 N, there is a transition from palmqvist to median crack due to the plastic deformation of the crystal. Controllable magnetic and mechanical characteristics will help to enhance performance of magnetic devices.</p>
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T. Ozeki, D. Yamamoto, G. Egawa, and S. Yoshimura
Journal of the Magnetics Society of Japan ( 日本磁気学会 ) 46 ( 3 ) 64 - 69 2022年05月 [査読有り]
研究論文（学術雑誌） 国内共著
<p> High saturation magnetization and perpendicular magnetic anisotropy are required for ferromagnetic / ferroelectric thin films to apply magnetic recording such as magnetic writing elements of magnetic wire memory, which is a next-generation device with very high recording density. To realize the magnetic properties, substitution of Co against Fe in (Bi<sub>1-x</sub>Bax)FeO<sub>3</sub> and (Bi<sub>1-x</sub>La<sub>x</sub>)FeO<sub>3</sub> thin films were investigated. In the (Bi,Ba)(Fe,Co)O<sub>3</sub> thin films, both Ba and Co substitution up to several tens at% had contribution to increase the saturation magnetization. The high saturation magnetization was obtained in (Bi,Ba)(Fe,Co)O<sub>3</sub> thin films with the total composition of Ba and Co of around 60 at%. Further increment of Ba and Co substitution decreased the saturation magnetization because the formation of the BiFeO<sub>3</sub> phase is hindered by an excess amount of Ba and Co with larger ion radius than Bi and Fe. Co substitution up to 20 at% had contribution to increase the perpendicular magnetic anisotropy. In the (Bi,La)(Fe,Co)O<sub>3</sub> thin films, the effect of La substitution was not large to increase the saturation magnetization and perpendicular magnetic anisotropy, however the effect of Co substitution up to 30 at% was large to increase the saturation magnetization and perpendicular magnetic anisotropy.</p>
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超常磁性Co基グラニュラー薄膜の磁気特性の成膜速度依存性と新規反応性パルスDCスパッタリング成膜法の有用性の検討
小林 拓海, 中田 尭人, 江川 元太, 吉村 哲
日本素材物性学会誌 ( 日本素材物性学会 ) 32 ( 1_2 ) 22 - 27 2022年03月 [査読有り]
研究論文（学術雑誌） 国内共著
<p>The superparamagnetic thin films with a granular structure show a characteristic magnetization curve. In this study, Co-Al<sub>2</sub>O<sub>3</sub> granular thin films were fabricated by the sputtering method with normal DC source for Co deposition, RF source for Al<sub>2</sub>O<sub>3</sub> deposition, and pulsed DC reactive sputtering were used for fabrication of non-magnetic matrix of oxide or nitride of Al or Si. As a result, Co-Al<sub>2</sub>O<sub>3</sub> superparamagnetic thin films with high magnetization could be obtained with high deposition rate. Very high deposition rate was obtained for fabrication of oxide or nitride films of Al or Si using the pulsed DC reactive sputtering method. This deposition rate was 5 times larger than RF sputtering method. It is expected that a sputtering method with DC source for Co deposition and pulsed DC source for matrix deposition will be effective to realize very high magnetization in the superparamagnetic granular thin films.</p>
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(Bi,A)FeO3薄膜（A＝Ca,Sr,Ba（アルカリ土類金属））の結晶構造と磁気特性におよぼすレーザーアシスト加熱成膜・後アニールの効果
鈴木 陸, 尾関 拓海, 江川 元太, 吉村 哲
日本素材物性学会誌 ( 日本素材物性学会 ) 32 ( 1_2 ) 15 - 21 2022年03月 [査読有り]
研究論文（学術雑誌） 国内共著
<p>High saturation magnetization is required for BiFeO<sub>3</sub>-based multiferroic（ferromagnetic/ferroelectric）thin films to apply magnetic writing element of Racetrack Memory which is a nextgeneration magnetic recording device. A newly introduced laser-assisted heating system was used to form high quality（Bi, <i>A</i>）FeO<sub>3</sub>（<i>A</i>=Ca, Sr, Ba（alkaline earth metal））thin films. The maximum substrate temperature was increased from 695 to about 858℃ by using this laserassisted heating system combining with lamp heating system of sputtering equipment. In the case of（Bi, Ca）FeO<sub>3</sub> and（Bi, Sr）FeO<sub>3</sub> with the Ca or Sr substitution concentration of 50～ 60 at％ fabricated by using the laser-assisted heating system, the crystallinity was improved, but oxygen vacancy could not be suppressed. As the result, saturation magnetization was not large. In the case of（Bi, Ba）FeO<sub>3</sub> with the Ba substitution concentration of 50～60 at％ fabricated by using the laser-assisted heating system, oxygen vacancy could be suppressed. As the result, highest saturation magnetization of around 100 emu/cm<sup>3</sup> was obtained in（Bi, Ba）FeO<sub>3</sub> thin films.</p>
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M. V. Makarova, Y. Akaishi, Y. Suzuki, K. S. Rao, S. Yoshimura, H. Saito
Journal of Magnetism and Magnetic Materials ( Journal of Magnetism and Magnetic Materials ) 546 ( 10 ) 168755 2022年01月 [査読有り]
研究論文（学術雑誌） 国内共著
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Munusamy Kuppan, Daichi Yamamoto, Genta Egawa, Sivaperuman Kalainathan, Satoru Yoshimura
Scientific Reports ( Scientific Reports ) 11 11118-1 - 11118-8 2021年05月 [査読有り]
研究論文（学術雑誌） 国際共著
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反応性パルスDCスパッタリング成膜におけるBiFeO3系強磁性・強誘電薄膜の高品位作製の指針
武田 航太朗, 山本 大地, 吉村 哲
日本磁気学会論文特集号 ( 公益社団法人 日本磁気学会 ) 4 ( 2 ) 116 - 120 2020年09月 [査読有り]
研究論文（学術雑誌） 国内共著
<p> BiFeO<sub>3</sub> based thin films with ferromagnetism were fabricated by using a pulsed DC reactive sputtering method. Guidelines on sputtering targets for fabricating the films are discussed in regard to obtaining high-quality BiFeO<sub>3</sub> based thin films. By using a target with a low oxide content (low molar ratio of oxide) and thus good conductivity, it is possible to suppress the charging and arc discharge on the surface of the target and enable high-energy sputtering. As a result, high-quality BiFeO<sub>3</sub> based thin films with a high saturation magnetization were formed. By using a target with a high oxygen content (including oxides with a high oxidation valence), the generation of oxygen vacancies that degrade the ferroelectric properties is suppressed, and pinning sites that suppress domain wall movement are then also suppressed. As a result, high-quality BiFeO<sub>3</sub> based thin films with good ferromagnetic properties could be formed.</p>
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Makarova, Y. Akaishi, T. Ikarashi, K. S. Rao, S. Yoshimura, and H. Saito
Journal of Magnetism and Magnetic Materials ( Journal of Magnetism and Magnetic Materials ) 471 209 - 214 2019年02月 [査読有り]
研究論文（学術雑誌） 国内共著
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Fu Zheng, Satoru Yoshimura, Shinya Yasui, Genta Egawa, and Hitoshi Saito
Journal of the Magnetics Society of Japan ( Journal of the Magnetics Society of Japan ) 43 ( 1 ) 6 - 10 2019年01月 [査読有り]
研究論文（学術雑誌） 国内共著
<p> High coercivity FePt•MgO films were successfully synthetized on cone-shape Si tips in a very high frequency (VHF) plasma irradiation-assisted magnetron sputtering system to prepare the MFM tips for evaluation of the AC magnetic field of perpendicular magnetic write head at high write current. Alloying with MgO significantly enhanced the coercivity of the magnetic coating due to the isolation of FePt grains by MgO. As a result, a high coercivity close to 20 kOe was achieved. The AC magnetic field images of the perpendicular magnetic write head at high write current were taken on alternating MFM (A-MFM) by this tip. A clear amplitude image with a strong signal at the main pole position was observe compared to the pure FePt layer-coated tip, which gave a blurry image and very small amplitude. Fourier analysis of the images obtained by this kind of FePt•MgO tip gives a spatial resolution of about 15 nm in air atmosphere. It is clear that the cone-shape FePt•MgO-coated MFM tip with a coercivity higher than the magnetic field to be measured is effective and capable for measuring the high AC magnetic field for an HD perpendicular magnetic write head at a very high write current.</p>