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Miyashita A, Maekawa M, Shimoyama Y, Seko N, Kawasuso A, Umetsu RY. High-density magnetic-vacancy inclusion in Co 2MnGa single crystal probed by spin-polarized positron annihilation spectroscopy. J Phys Condens Matter 2021; 34:045701. [PMID: 34695811 DOI: 10.1088/1361-648x/ac3304] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Accepted: 10/25/2021] [Indexed: 06/13/2023]
Abstract
Co2MnGa is a Weyl semimetal exhibiting giant anomalous Hall and Nernst effects. Using spin-polarized positron annihilation spectroscopy, we examined a Bridgman-grown Co2MnGa single crystal with a nearly perfectL21-ordered structure and a reference Co2MnAl polycrystal with a Mn-Al-disorderedB2 structure. We found that a large amount of magnetic vacancies (more than 100 ppm) were included in the Co2MnGa crystal but not the Co2MnAl crystal. We discuss possible reasons for the inclusion of vacancies, the role of vacancies in the development of the ordered structure, and the electronic states associated with the vacancies. Toward the development of Co2MnGa-based devices, the manners for reducing vacancies as well as the influence of vacancies on the electrical transport properties should be considered.
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Affiliation(s)
- A Miyashita
- National Institutes for Quantum and Radiological Science and Technology, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan
| | - M Maekawa
- National Institutes for Quantum and Radiological Science and Technology, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan
| | - Y Shimoyama
- National Institutes for Quantum and Radiological Science and Technology, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan
| | - N Seko
- National Institutes for Quantum and Radiological Science and Technology, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan
| | - A Kawasuso
- National Institutes for Quantum and Radiological Science and Technology, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan
| | - R Y Umetsu
- Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Sendai, Miyagi 980-8577, Japan
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Maekawa M, Miyashita A, Sakai S, Li S, Entani S, Kawasuso A, Sakuraba Y. Spin-Polarized Positronium Time-of-Flight Spectroscopy for Probing Spin-Polarized Surface Electronic States. Phys Rev Lett 2021; 126:186401. [PMID: 34018791 DOI: 10.1103/physrevlett.126.186401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2020] [Accepted: 03/25/2021] [Indexed: 06/12/2023]
Abstract
The energy spectrum of positronium atoms generated at a solid surface reflects the electron density of states (DOS) associated solely with the first surface layer. Using spin-polarized positrons, the spin-dependent surface DOS can be studied. For this purpose, we have developed a spin-polarized positronium time-of-flight spectroscopy apparatus based on a ^{22}Na positron source and an electrostatic beam transportation system, which enables the sampling of topmost surface electrons around the Γ point and near the Fermi level. We applied this technique to nonmagnetic Pt(111) and W(001), ferromagnetic Ni(111), Co(0001) and graphene on them, Co_{2}FeGa_{0.5}Ge_{0.5} (CFGG) and Co_{2}MnSi (CMS). The results showed that the electrons of Ni(111) and Co(0001) surfaces have characteristic negative spin polarizations, while these spin polarizations vanished upon graphene deposition, suggesting that the spin polarizations of graphene on Ni(111) and Co(0001) were mainly induced at the Dirac points that were out of range in the present measurement. The CFGG and CMS surfaces also exhibited only weak spin polarizations suggesting that the half-metallicity expected for these bulk states was not maintained at the surfaces.
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Affiliation(s)
- M Maekawa
- National Institutes for Quantum and Radiological Science and Technology, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan
| | - A Miyashita
- National Institutes for Quantum and Radiological Science and Technology, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan
| | - S Sakai
- National Institutes for Quantum and Radiological Science and Technology, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan
| | - S Li
- National Institutes for Quantum and Radiological Science and Technology, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan
| | - S Entani
- National Institutes for Quantum and Radiological Science and Technology, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan
| | - A Kawasuso
- National Institutes for Quantum and Radiological Science and Technology, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan
| | - Y Sakuraba
- National Institute for Materials Science (NIMS), 1-2-1, Sengen, Tsukuba-city, Ibaraki 305-0047, Japan
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Kawasuso A, Wada K, Miyashita A, Maekawa M, Iwamori H, Iida S, Nagashima Y. Positronium formation at 4H SiC(0001) surfaces. J Phys Condens Matter 2020; 33:035006. [PMID: 33017809 DOI: 10.1088/1361-648x/abbe7a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2020] [Accepted: 10/05/2020] [Indexed: 06/11/2023]
Abstract
Positronium formation at 4H SiC(0001) surfaces were investigated upon the removal of natural oxide layers by hydrofluoric acid etching and heat treatment at 1000 K in ultra-high vacuum. Two types of positronium were observed in the positronium time-of-flight (PsTOF) measurements irrespective of conduction type and surface polarity. One type formed the major part of the PsTOF spectrum with a maximum energy of 4.7 ± 0.3 eV. This energy exceeded the theoretical value calculated with valence electrons. The PsTOF spectrum shape was different from those of metal surfaces, suggesting that the surface state electrons or conduction electrons need to be considered as the positronium source. Another positronium appeared at 1000 K in the tail of the PsTOF spectrum with a maximum energy of 0.2-0.5 eV. This thermally-assisted athermal positronium may be formed via the surface state positrons and electrons.
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Affiliation(s)
- A Kawasuso
- National Institutes for Quantum and Radiological Science and Technology, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan
| | - K Wada
- National Institutes for Quantum and Radiological Science and Technology, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan
| | - A Miyashita
- National Institutes for Quantum and Radiological Science and Technology, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan
| | - M Maekawa
- National Institutes for Quantum and Radiological Science and Technology, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan
| | - H Iwamori
- Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan
| | - S Iida
- Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan
| | - Y Nagashima
- Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan
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Mochizuki I, Ariga H, Fukaya Y, Wada K, Maekawa M, Kawasuso A, Shidara T, Asakura K, Hyodo T. Structure determination of the rutile-TiO2(110)-(1 × 2) surface using total-reflection high-energy positron diffraction (TRHEPD). Phys Chem Chem Phys 2016; 18:7085-92. [DOI: 10.1039/c5cp07892j] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Detailed structure of the rutile-TiO2(110)-(1 × 2) has been determined using the newly developed technique of total-reflection high-energy positron diffraction (TRHEPD).
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Affiliation(s)
- I. Mochizuki
- Institute of Materials Structure Science
- High Energy Accelerator Research Organization (KEK)
- Ibaraki 305-0801
- Japan
| | - H. Ariga
- Institute for Catalysis
- Hokkaido University
- Sapporo
- Japan
| | - Y. Fukaya
- Advanced Science Research Center
- Japan Atomic Energy Agency
- Naka
- Japan
| | - K. Wada
- Institute of Materials Structure Science
- High Energy Accelerator Research Organization (KEK)
- Ibaraki 305-0801
- Japan
| | - M. Maekawa
- Quantum Beam Science Directorate
- Japan Atomic Energy Agency
- Takasaki
- Japan
| | - A. Kawasuso
- Quantum Beam Science Directorate
- Japan Atomic Energy Agency
- Takasaki
- Japan
| | - T. Shidara
- Accelerator Laboratory
- High Energy Accelerator Research Organization (KEK)
- Tsukuba
- Japan
| | - K. Asakura
- Institute for Catalysis
- Hokkaido University
- Sapporo
- Japan
| | - T. Hyodo
- Institute of Materials Structure Science
- High Energy Accelerator Research Organization (KEK)
- Ibaraki 305-0801
- Japan
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Li H, Maekawa M, Kawasuso A, Tanimura N. Effect of magnetic field on positron lifetimes of Fe, Co and Ni. J Phys Condens Matter 2015; 27:246001. [PMID: 26037478 DOI: 10.1088/0953-8984/27/24/246001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Positron lifetime spectra of Fe, Co and Ni were measured under magnetic field using a (22)Na source. Very small but distinguishable difference of positron lifetime upon magnetic field reversal was observed suggesting the existence of two bulk lifetimes associated with majority and minority spin electrons. Using two spin-dependent Fe bulk lifetimes, the difference Doppler broadening of annihilation radiation spectra between majority and minority spin electrons were also examined. Agreement between experiment and theory indicates that spin-polarized positron annihilation spectroscopy may have potential in investigation of spin-aligned electron momentum distribution.
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Affiliation(s)
- H Li
- Advanced Science Research Center, Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma JP-370-1292, Japan
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Zhang HJ, Yamamoto S, Gu B, Li H, Maekawa M, Fukaya Y, Kawasuso A. Charge-to-Spin Conversion and Spin Diffusion in Bi/Ag Bilayers Observed by Spin-Polarized Positron Beam. Phys Rev Lett 2015; 114:166602. [PMID: 25955066 DOI: 10.1103/physrevlett.114.166602] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2015] [Indexed: 06/04/2023]
Abstract
Charge-to-spin conversion induced by the Rashba-Edelstein effect was directly observed for the first time in samples with no magnetic layer. A spin-polarized positron beam was used to probe the spin polarization of the outermost surface electrons of Bi/Ag/Al2O3 and Ag/Bi/Al2O3 when charge currents were only associated with the Ag layers. An opposite surface spin polarization was found between Bi/Ag/Al2O3 and Ag/Bi/Al2O3 samples with the application of a charge current in the same direction. The surface spin polarizations of both systems decreased exponentially with the outermost layer thickness, suggesting the occurrence of spin diffusion from the Bi/Ag interface to the outermost surfaces. This work provides a new technique to measure spin diffusion length.
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Affiliation(s)
- H J Zhang
- Advanced Science Research Center, Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan
| | - S Yamamoto
- Quantum Beam Science Directorate, Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan
| | - B Gu
- Advanced Science Research Center, Japan Atomic Energy Agency, 2-4 Shirakata Shirane, Tokai-mura, Ibaraki 319-1195, Japan
| | - H Li
- Advanced Science Research Center, Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan
| | - M Maekawa
- Advanced Science Research Center, Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan
| | - Y Fukaya
- Advanced Science Research Center, Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan
| | - A Kawasuso
- Advanced Science Research Center, Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan
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Fukaya Y, Maekawa M, Mochizuki I, Wada K, Hyodo T, Kawasuso A. Reflection high-energy positron diffraction study on the first surface layer. ACTA ACUST UNITED AC 2014. [DOI: 10.1088/1742-6596/505/1/012005] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Hyodo T, Fukaya Y, Maekawa M, Mochizuki I, Wada K, Shidara T, Ichimiya A, Kawasuso A. Total reflection high-energy positron diffraction (TRHEPD). ACTA ACUST UNITED AC 2014. [DOI: 10.1088/1742-6596/505/1/012001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Wada K, Hyodo T, Kosuge T, Saito Y, Ikeda M, Ohsawa S, Shidara T, Michishio K, Tachibana T, Terabe H, Suzuki RH, Nagashima Y, Fukaya Y, Maekawa M, Mochizuki I, Kawasuso A. New experiment stations at KEK Slow Positron Facility. ACTA ACUST UNITED AC 2013. [DOI: 10.1088/1742-6596/443/1/012082] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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