| Project/Area Number |
09450231
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Physical properties of metals
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| Research Institution | TOHOKU UNIVERSITY |
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Principal Investigator |
SHIMADA Yutaka Research Institute for Scientific Measurements, Tohoku University, Professor, 科学計測研究所, 教授 (00006157)
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| Co-Investigator(Kenkyū-buntansha) |
OHTANI Yosichika Faculty of Engineering, Tohoku University, Ass. Professor, 工学部, 助教授 (60245610)
KITAKAMI Osamu Research Institute for Scientific Measurements, Tohoku University, Ass.Professor, 科学計測研究所, 助教授 (70250834)
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| Project Period (FY) |
1997 – 1999
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| Project Status |
Completed (Fiscal Year 1999)
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| Budget Amount *help |
¥13,000,000 (Direct Cost: ¥13,000,000)
Fiscal Year 1999: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 1998: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 1997: ¥10,600,000 (Direct Cost: ¥10,600,000)
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| Keywords | ultrafine particles / superparamagnetism / surface anisotropy / domain observation / ferromagnet |
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| Research Abstract |
Ferromagnetic materials lose their magnetic functions if their sizes decrease down to several nanometers because of emerging of the superparamagnetism. High resolution observation of magnetic domains which has been our original purpose can be achieved if synthesis of nm size ferromagnetic particles with high magnetic energy which overcomes superparamagnetism is developed. In this research developing of high energy particles by alloying and producing a high surface energy was studied. The following are the results.
Co particles were produced by condensation in rare gas with stable fcc phase with the size smaller than 10nm, but hcp phase is semi-stable for these sizes. The mechanism governing this process is from the surface free energy of the particles which takes a variety of crystal shapes.
To stabilize hcp phase in the particles Co-Pt particles were produced in the same way. Higher condensation of hcp phase particles were confirmed. The anisotropy energy obtained by the direct measurem
… More
ent of these particles is extra-ordinarily high in comparison with that of the bulk material. This strongly suggests that a surface anisotropy associated with the particle surface is taking a dominant role.
Rare earth-transition metal particles were produced and the magnetism was studied. However, the particles were not chemically stable due to oxidation. The rate of instability could be reduced appreciably by overcoating the particles, but high coercivity was not attained. The possible reason for this peculiar phenomena is invasion of oxygen into the particles bodies destroying the surface smoothness which is inevitable for high surface energy. The investigation was terminated at this stage because of the difficulty mentioned above.
Multilayers and granular films consisting of transition metal and oxides were synthesized and a method to evaluate the genuine surface anisotropy was developed. One of the valuable results is that the interface of Co/MgO multilayer has a very high surface anisotropy.
Summarizing these results, the high energy particles which have been a purpose of the research from the start were obtained in Co-Pt system with the size down to 10nm and a high surface energy was confirmed. This provides us with a valuable suggestion that particles with higher surface energy can be synthesized by chemical reconstruction of the particle surface. Less
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