| Project/Area Number |
14076202
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| Research Category |
Grant-in-Aid for Scientific Research on Priority Areas
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| Allocation Type | Single-year Grants |
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| Review Section |
Science and Engineering
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| Research Institution | Tohoku University |
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Principal Investigator |
INOMATA Koichiro Tohoku University, Graduate School of Engineering, Professor, 大学院工学研究科, 教授 (90323071)
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| Co-Investigator(Kenkyū-buntansha) |
TEZUKA Nobuki Tohoku University, Graduate School of Engineering, Research Associate, 大学院工学研究科, 助手 (40323076)
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| Project Period (FY) |
2002 – 2005
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| Project Status |
Completed (Fiscal Year 2005)
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| Budget Amount *help |
¥19,700,000 (Direct Cost: ¥19,700,000)
Fiscal Year 2005: ¥2,600,000 (Direct Cost: ¥2,600,000)
Fiscal Year 2004: ¥4,300,000 (Direct Cost: ¥4,300,000)
Fiscal Year 2003: ¥4,800,000 (Direct Cost: ¥4,800,000)
Fiscal Year 2002: ¥8,000,000 (Direct Cost: ¥8,000,000)
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| Keywords | Spin resonance tunneling effect / Double tunneling junctions / Epitaxy / Conductance oscillation / Spin dependent quantum well / Heusler alloy / Tunnel junction / Tunnel magnetoresistance / スピン依存量子準位 / ホイスラー合金薄膜 / スピン分極率 / 強磁性トンネル効果 / L2_1構造 / MRAM / 磁気抵抗比 / ナノサイズ素子 / トンネル磁気抵抗効果 / 磁気モーメント / 反平行結合素子 / 不揮発性固体磁気メモリ / スピン反転磁場 / 反平行結合膜 / 磁気力顕微鏡 |
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| Research Abstract |
We have investigated the creation of the spin dependent resonant tunneling devices and the tunnel magnetoresistance of ferromagnetic tunnel junctions (MTJs) using half metallic full-Heusler alloys. Epitaxial double barrier ferromagnetic tunnel junctions (DBTJs) consisting of Fe/MgO/Fe/MgO/Fe were fabricated of a MgO substrate using MBE for the former, in which the intermediate Fe layer thickness was changed. As a result, we have observed the oscillation of the differential conductance as a function of bias voltage for the first time. The oscillation was observed even at RT, although its amplitude was decreased with increasing temperature. The oscillation period increased with decreasing Fe layer thickness. These phenomena are understood by the formation of the quantum well states of Ai band in the middle Fe layer. The TMR is over 100% at RT due to the coherent tunneling and the bias voltage dependence of the TMR is more gentle than that of the single barrier junction and V_<1/2>=1.4 V.
For the latter we have studied MTJs using Co_2(Cr_<1-x>Fe_x)Al (CCFA) and concluded that L2_1 structure is difficult to be obtained, which leads to lower spin polarization than that of the calculation. The maximum TMR is 83% at 5K and 54% at RT for x=0.6. We have investigated another Heusler alloy system of Co_2Fe(Al_ySi_<1-y>) and resulted in the observation of the L2_1 structure and integer magnetic moment of 6ujb for Co_2FeSi, suggesting half metallic. The TMR, however, is only 40% at RT for the MTJ using a Co_2FeSi. The maximum TMR at present is 60% at RT for x=0.5 with B2 structure. The further study will lead to higher TMR.
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