2000 Fiscal Year Final Research Report Summary
Study of π phase for superconducting superlattices with ferromatnetic layers
| Project/Area Number |
10640324
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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 | Tohoku University |
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Principal Investigator |
TAKANAKA Kenji Tohoku University, Graduate School of Engineering, Professor, 大学院・工学研究科, 教授 (80005321)
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| Project Period (FY) |
1998 – 2000
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| Keywords | superconductor / ferromgnet / superlattice / π phase / transition temperature / upper critical field / G-L equations |
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| Research Abstract |
Some experimental observations show that the transition temperature T_c(d_f) has a minimum as a function of the thickness d_f of the ferromagnetic layer for the fixed thickness of the superconducting layer. This is due to the occurence of the π phase, that is, the phase difference of the pair function between the two ferromagnetic layers changes by π. We pointed out that the strength of the exchange interaction is important and calculated the critical temperature T_c and the upper critical field H_<c2>.
The above quantities such as T_c and H_<c2> are determined by the linear order of the order parameter. Far from the transition temperature and the upper critical field, the nonlinear term of the order parameter are important. We have derived its analytical expression for the superconducting superlattices. Using the obtained term, we numerically calculated the κ_2 parameter, which expresses the temperature dependence of the magnetization.
Further angular dependence of the upper critical field H_<c2> was derived for the superconducting superlattice with spatial variation of the diffucion constant D(z), where the magnetic field is applied nearly along the normal direction of layers. The results are applied to the recent observations for Nb/NbZr superlattice and we point out that the intrinsic properites of Nb/NbZr superlattice are important.
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