| Project/Area Number |
09640440
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
固体物性Ⅱ(磁性・金属・低温)
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| Research Institution | KYUSHU INSTITUTE OF TECHNOLOGY |
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Principal Investigator |
DEGUDHI Hiroyuki Kyushu Inst.Tech., Faculty of Engineerig, Associate prof., 工学部, 助教授 (30192206)
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| Co-Investigator(Kenkyū-buntansha) |
TAKAGI Seishi Kyushu Inst.Tech., Faculty of Engineering, Professor, 工学部, 教授 (90112359)
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| Project Period (FY) |
1997 – 1998
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| Project Status |
Completed (Fiscal Year 1998)
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| Budget Amount *help |
¥3,000,000 (Direct Cost: ¥3,000,000)
Fiscal Year 1998: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1997: ¥2,500,000 (Direct Cost: ¥2,500,000)
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| Keywords | Diluted antiferromagnet / Random systems / Griffiths phase / AC susceptibility / Cole-Cole plot / Slow dynamics / 希釈磁性体 / スローダイナミクス |
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| Research Abstract |
A nickel salt Ni(OH)_2 is a quasi-two-dimensional antiferrornagnet with the Neel temperature T_N=26,6K.In the ordered state, spins on the triangular lattice in the c-plane are paralled to the c-axis with strong ferromagnetic couplings. Interlayer weak antiferromagnetic couplings makes the spins on a layer ntiparallel to those on the adjacent layers. The magnetization measurements of the diluted magnet Ni_xMg_<1-x>(OH)_2 were done using a SQUID magnetometer. The field-cooled magnetization M_<FC> increases monotonically with decreasing temperature and begins to deviate from the zero-field-cooled magnetization M_<ZFC> at T_G which is higher than T_N. The time dependence of thermoremanent magnetization M_<TRM> was measured. The magnetization M_<TRM> relaxes slowly and fits well with a power law, which observed experimentally in spin-glass system and discussed theoretically on the basis of the unfrustrated clusters of spins. The complex ac susceptibility is measured as a function of the temperature and frequency. The results are analyzes in terms of the Cole-Cole formalism. The dynamics of relaxation above T_N is the slow-dynamics which is seen theoretically in the Griffiths phase of spin glass system. These experimental results suggest the existence of unfrustrated clusters of spins in Ni_xMg_<1-x>(OH)_2 even above T_N. In the temperature range T_N < T < T_G, such clusters may be in nearly ordered states and fluctuate with large relaxation times. Therefore, we have concluded that the slow relaxation in Ni_xMg_<1-x>(OH)_2 above T_N may result from the Griffiths phase.
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