2007 Fiscal Year Final Research Report Summary
Development of magnetic tunnel junctions using Heusler alloy and observation of spin-injected magnetization reversal
| Project/Area Number |
17206001
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Applied materials science/Crystal engineering
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| Research Institution | Tohoku University |
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Principal Investigator |
MIYAZAKI Terunobu Tohoku University, Graduate school of Engineering, Professor emeritus (60101151)
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| Co-Investigator(Kenkyū-buntansha) |
ANDO Yasuo Graduate school of Engineering, 大学院・工学研究科, Professor (60250726)
KUBOTA Hitoshi AIST, Nano-electronics Research Institute, Researcher (30261605)
MIZUKAMI Shigemi Nihon University, Faculty of Engineering, lecturer (00339269)
OOGANE Mikihiko Graduate school of Engineering, 大学院・工学研究科, Assistant Professor (50396454)
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| Project Period (FY) |
2005 – 2007
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| Keywords | Epitaxial Heusler alloy / Co_2MnSi / TMR ratio / Energy gap / Micro-fabrication / Spin-injected magnetic reversal / Switching current / Damping constant |
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| Research Abstract |
1. Fabrication of magnetic tunnel junctions using epitaxial Heusler alooy electrodes Large tunnel magneto-resistance (TMR) ratios of 217% at room temperature and 753% at low temperature have been successfully observed in a magnetic tunnel junction (MTJ) using a high quality Heusler alloy electrode and an MgO crystalline barrier. The structure of the MTJ was Co2MnSi/MgO/CoFe. This observed TMR ratio is highest among the MTJs using Heusler alloy electrodes. Moreover, conductance-voltage property of the MTJ investigated in detail indicates that the origin of the large TMR was coherent tunneling process through the crystalline MgO barrier.
2. Micro-fabrication of MTJs and Observation of spin-injected magnetization reversal Spin-injected magnetization reversal has been successfully observed in the micro-fabricated CoFeB/MgO/CoFeB-MTJs using (Co_<50>Fe_<50>)_<100-x>B_x (x=20, 25, 30, thickness d=2 nm) switching layers. We found from this result that the switching current density depended on magnetization, damping constant and spin polarization of the ferromagnetic layer as expected by theory and reducing of magnetization and damping constant was quite effective to decrease the switching current density.
3. Magnetic damping constant α Magnetic damping constants in various ferromagnetic thin films were investigated systematically by FMR technique. Moreover, a measurement technique for estimation of damping constants in MTJs has been established. As a result, we found that the damping constant of 2nm thick CoFeB film was five times larger than that of bulk CoFeB and the neighboring layer of the switching layer influence the damping constant of the switching layer.
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