| 研究課題/領域番号 |
20J22909
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| 研究機関 | 大阪大学 |
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研究代表者 |
Wicaksono Yusuf 大阪大学, 基礎工学研究科, 特別研究員(DC1)
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| 研究期間 (年度) |
2020-04-24 – 2023-03-31
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| キーワード | graphene (Gr) / magnetoresistance (MR) / Dirac cone engineering / ultimate MR ratio / Gr-hBN heterostructure / hBN-Gr-hBN MTJ / new MTJ mechanism |
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| 研究実績の概要 |
A transmission probability calculation on two proposed spintronic devices based on 2D materials, Ni/graphene/Ni and Ni/hBN-graphene-hBN/Ni, was performed. For Ni/graphene/Ni system, graphene layer which partly sandwiched with Ni slabs is considered. Two magnetic alignments of Ni slabs were considered, anti-parallel configuration (APC) and parallel configuration (PC). The in-plane conductance calculation of graphene is performed. The result showed in-plane magnetoresistance (MR) ratio of graphene is up to 1450%. This MR ratio is the highest MR ratio found for the case of graphene spintronic devices. The high MR ratio is originated from the opening and closing of the gapped Dirac cone, which is controllable through the magnetic alignment of Ni slabs. The gapped Dirac cone is open and close when the magnetic alignment of Ni slabs in APC and PC, respectively. This high TMR comes from a finite size atomic-scale width Ni slabs. If Ni slabs in nanometer-scale width are considered, an ultimate MR ratio is expected from the system. On the other hand, our investigation on Ni/hBN-graphene-hBN/Ni magnetic tunnel junction (MTJ) also showed beyond expectation results. A tunneling magnetoresistance (TMR) ratio as high as 1200% was found when the transmission of the excited electrons is considered. This high TMR originates from the transmission of Ni surface states and enhances through the proximity effect on the graphene layer. A device design with a new reading process mechanism by using light irradiation was proposed. This new mechanism could not be found in the conventional MTJ.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
1: 当初の計画以上に進展している
理由
First-principles quantum transport calculations, which couples density functional theory (DFT) with the non-equilibrium Green’s function (NEGF) within Landauer-Buttiker (LB) formalism, were performed to calculate the conductance of the system. This sophisticated calculation is beyond our original plan, where previously the transmission probability calculation by only using DFT-LB is expected. The high accuracy of this calculation leads to the finding of an ultimate in-plane magnetoresistance ratio of graphene when it partly sandwiched with Ni slabs is observed. On the other hand, the proposed 2D materials magnetic tunnel junction (MTJ), Ni/hBN-Gr-hBN/Ni, showed TMR as high as ~1200% which is higher than conventional one. The new reading mechanism of the MTJ device was also proposed.
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| 今後の研究の推進方策 |
Controlling the gapped Dirac cone via pseudospin through proximity effect is considered. The investigation on the influence of proximity effect from ferromagnetic insulator(FI) to graphene toward the induced magnetic moment due to localized state or edge state will be conducted. For the former part, induced magnetic moment in the localized state due to nitrogen doping or vacancy is considered. Meanwhile, for the later part, induced magnetic moment from zig-zag graphene nano-ribbon (ZGNR) is considered. The modified graphene, as well as ZGNR, is placed on FI. The magnetic properties and electronic structure of those systems will be investigated by using DFT-spin-GGA. The low-energy effective Hamiltonian approximation will be applied to investigate the proximity effect on zero-mode.
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