2022 Fiscal Year Annual Research Report
スピン分解ARPESによる遷移金属ダイカルコゲナイド磁性薄膜の研究
| Project/Area Number |
22J13684
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| Allocation Type | Single-year Grants |
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| Research Institution | Tohoku University |
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Principal Investigator |
Chuang ChienーWen 東北大学, 理学研究科, 特別研究員(DC2)
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| Project Period (FY) |
2022-04-22 – 2024-03-31
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| Keywords | 2D Ferromagnet / ARPES / XMCD / MBE |
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| Outline of Annual Research Achievements |
I have succeeded to grow monolayer (ML), multilayers of Cr2Se3 by molecule beam epitaxy (MBE) method and characterized the crystal structure by reflective high energy electron diffraction (RHEED) and low energy electron diffraction (LEED). To investigate the electronic and magnetic properties of Cr2Se3 ultrathin films, I carried out x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD), and angle resolved photoemission spectroscopy (ARPES). The Cr L edge (2p- 3d) of XAS and XMCD results showed a clear XMCD signal, indicating the ferromagnetism in ML Cr2Se3. The experimental XAS and XMCD spectra are in good agreement with the charge transfer cluster model calculation using Cr3+ configuration. The ARPES results of ML Cr2Se3 showed highly dispersive bands and tiny electron pocket at K points, which are consistent with first principles calculations. Further, temperature-dependence of band structure showed dramatic momentum-dependent band splitting and band structure change below the ferromagnetic transition. Surprisingly, the intensities of electron pockets also showed systematic increase when reducing T. This kind of band structure changes across Curie temperature (Tc) were also observed in multiplayer of Cr2Se3 in which Tc is reduced compared to the ML case. The unusual band structure evolution cannot be simply explained in terms of the exchange coupling. I concluded that consideration of strong pd hybridization and spin-orbit coupling (S.O.C) as well as electron carrier density is necessary to understand the ferromagnetism of Cr2Se3 ultrathin films.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
The research of my PhD work are going well, because the required instruments for Cr2Se3 thin film growth by MBE are well equipped and operated in the lab. I don't have much difficulties for accessing the machine. Also, I got enough time and chance to do XAS, XMCD and ARPES measurements at synchrotron radiation institutes in Japan. Further, the intensive discussion with supervisor was helpful for me to understand the scientific part of my PhD work and how to proceed the measurement at each stages.
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| Strategy for Future Research Activity |
According to the band structure calculation of ML Cr2Se3 which predict it as a 2D half metal, the electron pocket shows full spin polarization. This makes it very useful for developing the spintronic devices. It is important to investigate the spin-resolved band structure to realize the half metallicity of ML Cr2Se3. Since the present results of ML and multilayer of Cr2Se3 showed systematic reduction of Tc as estimated from the T-dependent ARPES results, I will carry out the magneto-optic Kerr effect (MOKE) to estimate more precisely the Curie temperature of Cr2Se3 ultra thin film,. Moreover, I am planning to determine topography of thin films and the local density of states in real space by scanning tunneling microscope.
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