2001 Fiscal Year Final Research Report Summary
STUDY OF QUANTUM TUNNELING EFFECT IN NANOSCALE MAGNET BY NUCLEAR MAGNETIC RESONANCE
| Project/Area Number |
11440106
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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 |
固体物性Ⅱ(磁性・金属・低温)
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| Research Institution | KYOTO UNIVERSITY |
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Principal Investigator |
GOTO Takao KYOTO UNIVERSITY, GRADUATE SCHOOL OF HUMAN AND ENVIRONMENTAL STUDIES, PROFESSOR, 大学院・人間・環境学研究科, 教授 (90026807)
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| Co-Investigator(Kenkyū-buntansha) |
KUBO Takeji NARA UNIVERSITY OF EDUCATION, PROFESSOR, 教授 (00031576)
MIYASHITA Seiji UNIVERSITY OF TOKYO, GRADUATE SCHOOL OF TECHNOLOGY, PROFESSOR, 大学院・工学研究科, 教授 (10143372)
OYAMADA Akira KYOTO UNIVERSITY, GRADUATE SCHOOL OF HUMAN AND ENVIRONMENTAL STUDIES, ASSISTANT, 大学院・人間・環境学研究科, 助手 (60211835)
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| Project Period (FY) |
1999 – 2001
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| Keywords | nano-scale molecular magnet / Mn_<12>-acetate / ^<55>Mn NMR / nuclear magnetic resonance / quantum tunneling / V_<15> |
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| Research Abstract |
The purpose of the present projects is to clarify the quantum tunneling effect and relevant spin dynamics from the microscopic view point using NMR on the typical nano-scale molecular magnets Mn_<12>Ac and V_<15>. Using high frequency pulsed powander amplifier and He3 NMR cryostat purchased in 2000 and 2001, we constructed high frequency NMR apparatus up to 800MHz operating at very low temperatures.
On Mn_<12>Ac, after the first success in observation of ^<55>Mn NMR and determination of the hyperfine interactions of the ^<55>Mn in three nonequivalent Mn^<+4> and Mn^<+3> ions, we have studied the followings: (1) The experimental T_2 and T_1 below 2.5K and down to 0.5K in the field s up to 8T were analyzed by considering the thermal fluctuation of Zeeman levels of the cluster spin by spin -phonon interaction within the framework of the ground-state and the first excited state. It turns out that 1/T_2 is interpreted in terms of strong collision model, while 1/T_1 is well understood via standard perturbation formalism. (2) From the measurement of the spin-echo signal intensity, we found that the recovery of the cluster magnetization exhibits √<t> -behavior during the initial short time, and there appear dips at every 0.45T, which indicates the evidence for the quantum tunneling. (3) At ultra-low temperatures there happens an avalanche effect.
On V_<15>, the temperature dependence of 1/T_1 of proton in the various values of the applied field has been interpreted in terms of thermal-activated model reflecting the simple Zeeman levels constructed from the ground state of S=1/2 and S=3/2.
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