| Co-Investigator(Kenkyū-buntansha) |
TOHJI Kazuyuki TOHOKU UNIVERSITY, GRADUATE SCHOOL OF ENVIRONMENTAL STUDIES, PROFESSOR, 大学院・環境科学研究科, 教授 (10175474)
SHINODA Kozo TOHOKU UNIVERSITY, GRADUATE SCHOOL OF ENVIRONMENTAL STUDIES, LECTURER, 大学院・環境科学研究科, 講師 (10311549)
SATO Yoshinori TOHOKU UNIVERSITY, GRADUATE SCHOOL OF ENVIRONMENTAL STUDIES, LECTURER, 大学院・環境科学研究科, 助手 (30374995)
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| Budget Amount *help |
¥9,100,000 (Direct Cost: ¥9,100,000)
Fiscal Year 2004: ¥2,600,000 (Direct Cost: ¥2,600,000)
Fiscal Year 2003: ¥6,500,000 (Direct Cost: ¥6,500,000)
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| Research Abstract |
In this project, the synthesis of magnetic metal and alloy nanoparticles by using the chemical method called "polyol process" was investigated in detail. The reaction parameters such as type of polyol, synthesis temperature, metal ion concentration, reaction promoting agents, and nucleating agents were effectively utilized to control the reaction kinetics to obtain magnetic nanoparticles with required physical properties such as size and crystal structure. This paved the way for the synthesis of magnetic nanoparticles with varying magnetic properties. For example in the cases of transition metal nanoparticles such as cobalt and nickel, the synthesis of particles with diameters ranging from few micron to few tens of nanometer and varying crystal structures was realized. For example, the bulk cobalt is known to have fcc phase at temperatures as high as 421.5℃. However, the cobalt metal particles synthesized using the modified polyol process were found to posses fcc structure at micron si
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ze levels. When the reaction kinetics was enhanced, the particle size was reduced to submicron and even to few tens of nanometer. Along with size reduction, the crystal structure also changed from fcc at micron size range, coexistence of fcc and hcp in the submicron size range and to s and hcp cobalt at nanometer size range. On the other hand, we also succeeded in the synthesis of non-magnetic hcp-Ni nanoparticle of few tens of nanometer in diameter.
In the case of the synthesis of magnetic alloy nanoparticles for magnetic recording, we have successfully demonstrated the direct synthesis of L1_0 FePt nanoparticles at low temperature of 553 K using "modified polyol method" without subsequent annealing, whose diameter is 5-10 nm and the intrinsic magnetocrystalline anisotropy field (H_k) is 31 kOe. This indicates that precise control of the reaction kinetics, especially low reduction rate through optimizing the polyol/Pt salt mole ratio and type of polyol are very important for directly synthesizing the L1_0 FePt nanoparticles. CoPt nanoparticles with high magnetocrystalline anisotropy and also particle sizes of 7 nm in diameter were prepared by using the modified polyol process. Furthermore, we also succeeded in selectively fixing FePt and CoPt nanoparticles on a silicon substrate by using APTS as the coupling layer, which prevents the grain growth even at higher annealing temperatures. Though the presence of the highly anisotropic phases was identified the potential of the particles were well below the anticipated values. Although the successful fabrication of recording media using magnetic particles for portable compact memory was not realized, considerable information and knowledge related to both the synthesis of nanoparticles and the fabrication of nanoparticle monolayer film was gathered. Thus, using this information as the base, we will work towards the development of high-density recording medium. Less
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