2021 Fiscal Year Annual Research Report
Theoretical Study of Spintronics Devices Based on Two-Dimensional Materials
| Project/Area Number |
20J22909
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| Research Institution | Osaka University |
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Principal Investigator |
Wicaksono Yusuf 大阪大学, 基礎工学研究科, 特別研究員(DC1)
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| Project Period (FY) |
2020-04-24 – 2023-03-31
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| Keywords | graphene (Gr) / Gr-hBN heterostructure / Dirac cone engineering / spin-mechatronic / proximity effect |
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| Outline of Annual Research Achievements |
The magnetoresistance changes beyond the charge neutrality point in Ni/graphene/Ni can be overcome by several methods-one of them by introducing a gate voltage. However, the strong chemical bonding between Ni slabs and graphene led to a difficult control of graphene's Fermi energy using gate voltage. Thus, an insulator barrier needs to introduce between Ni slabs and graphene so that the electric field can make charge polarization at the surface of Ni slabs resulting in easier control of graphene's Fermi energy. Therefore, the hBN layer or adsorbed gas (AG) atoms such as H, O, F, P, or S atoms were introduced between the graphene and Ni slabs. As a result, the controllable induced magnetic moment on graphene was replaced through charge transfer to magnetic proximity effect. Thus, the investigation of controllable graphene's mass-gapped Dirac cone (MGDC) through the magnetic proximity effect was conducted. Ni/hBN-graphene-hBN/Ni and Ni/X-graphene-X/Ni (with X being AG atom) nano-spin-valve were considered. A comparable size of MGDC compared to Ni/graphene/Ni was found on Ni/O-graphene-O/Ni. On the other hand, in Ni/hBN-graphene-hBN/Ni, a controllable MGDC size of graphene was observed by introducing a translational mechanical motion of Ni/hBN slabs. This method leads the system to exhibit three memory states. It opens the opportunity to create 2D materials-based magnetic junctions with a memory state of more than two states which cannot be found in the conventional magnetic tunnel junctions (MTJs).
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
The strategy to control the magnetoresistance changes beyond the charge neutrality point is within our original plan. A successful design by using O atoms as a barrier between Ni slabs and graphene creates a comparable performance but with easier control of Fermi energy. On the other hand, finding the possible three memory states through a translational mechanical motion of Ni/hBN slabs in Ni/hBN-graphene-hBN/Ni is beyond expectation. This finding opens the opportunity to control the gap size of graphene's MGDC by other methods that might create multi-level memory states. Furthermore, the preliminary result in local control of graphene-induced magnetic moment was found, which is beyond the original plan. This preliminary result might lead to a possible application on the neuromorphic device.
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| Strategy for Future Research Activity |
The effect of spin-orbit coupling on the in-plane conductance of graphene in Ni/graphene/Ni, Ni/hBN-graphene-hBN/Ni, and Ni/X-graphene-X/Ni (with X is adsorbed atomic gas) nano-spin-valve will be investigated:
1. The spin-orbit coupling strength will be examined by looking at Rashba coupling through electronic structure calculations. After that, the precision of induced magnetic moment on graphene will be studied through spin-charge density mapping. The investigation will be done through spin-GGA DFT.
2. Transmission probability calculation will be done using non-equilibrium Green's function within Landauer-Buttiker formalism to understand the effect of spin-orbit coupling on the in-plane conductance of graphene.
3. The voltage gate is considered to investigate the influence of the external electric field on the precision of induced magnetic moment on graphene.
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