Microstructure, magnetic and transport properties of a Mn2CoAl Heusler compound

X. D. Xu; Z. X. Chen; Y. Sakuraba; A. Perumal; K. Masuda; L. S.R. Kumara; H. Tajiri; T. Nakatani; J. Wang; W. Zhou; Y. Miura; T. Ohkubo; K. Hono

doi:10.1016/j.actamat.2019.06.047

Microstructure, magnetic and transport properties of a Mn₂CoAl Heusler compound

X. D. Xu, Z. X. Chen, Y. Sakuraba, A. Perumal, K. Masuda, L. S.R. Kumara, H. Tajiri, T. Nakatani, J. Wang, W. Zhou, Y. Miura, T. Ohkubo, K. Hono

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23 Citations (Scopus)

Abstract

We report a detailed analysis of microstructure, magnetic and transport properties of a stoichiometric Mn₂CoAl Heusler alloy, which has been predicted to be a spin-gapless semiconductor (SGS). Microstructure analysis revealed that the main phase was Mn_1.8Co_1.4Al_0.8 rather than Mn₂CoAl. Although conventional X-ray diffraction suggested the formation of single phase with XA/L2₁ strcture, a disk-shaped Mn-rich precipitate phase was observed in both annealed stoichiometric and Co-rich Mn₂CoAl alloys along with the Mn_1.8Co_1.4Al_0.8 main phase. Atomically resolved energy-dispersive X-ray spectroscopy mappings revealed that the Mn_1.8Co_1.4Al_0.8 phase has a disordered inverse XA Heusler structure with Mn (A) and Al (C) sites partially substituted by Co and Mn, respectively. First-principles calculations based on the observed disordered structure suggest that the Heusler phase is not SGS but half-metallic. However, both annealed stoichiometric and Co-rich Mn₂CoAl exhibit semiconducting-like resistivity and low anomalous Hall conductivity. These transport properties were regarded as the signatures of SGS in the previous studies; however, it could be due to localization of charged carriers due to the intersection of the Fermi level with Mn 3d and Co 3d states in Mn_1.8Co_1.4Al_0.8. This study demonstrates that not only measurements of transport properties but also careful microstructure inspections are essential to validate SGS properties in the theoretically predicted SGS candidates among Heusler compounds.

Original language	English
Pages (from-to)	33-42
Number of pages	10
Journal	Acta Materialia
Volume	176
DOIs	https://doi.org/10.1016/j.actamat.2019.06.047
Publication status	Published - 2019 Sept 1
Externally published	Yes

Keywords

Heusler alloys
Microstructure
Phase stability
Spin-gapless semiconductor
Transport properties

ASJC Scopus subject areas

Electronic, Optical and Magnetic Materials
Ceramics and Composites
Polymers and Plastics
Metals and Alloys

Access to Document

10.1016/j.actamat.2019.06.047

Cite this

@article{3ae51d0bdcf248e083916d3d680c14ef,

title = "Microstructure, magnetic and transport properties of a Mn2CoAl Heusler compound",

abstract = "We report a detailed analysis of microstructure, magnetic and transport properties of a stoichiometric Mn2CoAl Heusler alloy, which has been predicted to be a spin-gapless semiconductor (SGS). Microstructure analysis revealed that the main phase was Mn1.8Co1.4Al0.8 rather than Mn2CoAl. Although conventional X-ray diffraction suggested the formation of single phase with XA/L21 strcture, a disk-shaped Mn-rich precipitate phase was observed in both annealed stoichiometric and Co-rich Mn2CoAl alloys along with the Mn1.8Co1.4Al0.8 main phase. Atomically resolved energy-dispersive X-ray spectroscopy mappings revealed that the Mn1.8Co1.4Al0.8 phase has a disordered inverse XA Heusler structure with Mn (A) and Al (C) sites partially substituted by Co and Mn, respectively. First-principles calculations based on the observed disordered structure suggest that the Heusler phase is not SGS but half-metallic. However, both annealed stoichiometric and Co-rich Mn2CoAl exhibit semiconducting-like resistivity and low anomalous Hall conductivity. These transport properties were regarded as the signatures of SGS in the previous studies; however, it could be due to localization of charged carriers due to the intersection of the Fermi level with Mn 3d and Co 3d states in Mn1.8Co1.4Al0.8. This study demonstrates that not only measurements of transport properties but also careful microstructure inspections are essential to validate SGS properties in the theoretically predicted SGS candidates among Heusler compounds.",

keywords = "Heusler alloys, Microstructure, Phase stability, Spin-gapless semiconductor, Transport properties",

author = "Xu, {X. D.} and Chen, {Z. X.} and Y. Sakuraba and A. Perumal and K. Masuda and Kumara, {L. S.R.} and H. Tajiri and T. Nakatani and J. Wang and W. Zhou and Y. Miura and T. Ohkubo and K. Hono",

note = "Funding Information: This work was in part supported by the Grant-in-Aids for Scientific Research (S) (Grant No. 17H06152 ) from the Japan Society for the Promotion of Science and Scientific Innovation for Energy Harvesting Technology {"} ( JPMJCR16QS ), PRESTO from JST, Japan. The synchrotron XRD experiments were performed at the beamline BL13XU in SPring-8 with the approval of JASRI (Proposal Nos. 2017B1975 , 2018A1016 , and 2018A1503 ). AP acknowledges the Japan Society for the Promotion of Science for the provision of a JSPS fellowship . The authors would like to thank Varun Kumar Kushwaha, Kohei Hamaya, Shinya Yamada and Kenji Ueda for valuable discussions and Natsuko Kojima for technical supports. Publisher Copyright: {\textcopyright} 2019 Acta Materialia Inc.",

year = "2019",

month = sep,

day = "1",

doi = "10.1016/j.actamat.2019.06.047",

language = "English",

volume = "176",

pages = "33--42",

journal = "Acta Materialia",

issn = "1359-6454",

publisher = "Elsevier Limited",

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TY - JOUR

T1 - Microstructure, magnetic and transport properties of a Mn2CoAl Heusler compound

AU - Xu, X. D.

AU - Chen, Z. X.

AU - Sakuraba, Y.

AU - Perumal, A.

AU - Masuda, K.

AU - Kumara, L. S.R.

AU - Tajiri, H.

AU - Nakatani, T.

AU - Wang, J.

AU - Zhou, W.

AU - Miura, Y.

AU - Ohkubo, T.

AU - Hono, K.

N1 - Funding Information: This work was in part supported by the Grant-in-Aids for Scientific Research (S) (Grant No. 17H06152 ) from the Japan Society for the Promotion of Science and Scientific Innovation for Energy Harvesting Technology " ( JPMJCR16QS ), PRESTO from JST, Japan. The synchrotron XRD experiments were performed at the beamline BL13XU in SPring-8 with the approval of JASRI (Proposal Nos. 2017B1975 , 2018A1016 , and 2018A1503 ). AP acknowledges the Japan Society for the Promotion of Science for the provision of a JSPS fellowship . The authors would like to thank Varun Kumar Kushwaha, Kohei Hamaya, Shinya Yamada and Kenji Ueda for valuable discussions and Natsuko Kojima for technical supports. Publisher Copyright: © 2019 Acta Materialia Inc.

PY - 2019/9/1

Y1 - 2019/9/1

N2 - We report a detailed analysis of microstructure, magnetic and transport properties of a stoichiometric Mn2CoAl Heusler alloy, which has been predicted to be a spin-gapless semiconductor (SGS). Microstructure analysis revealed that the main phase was Mn1.8Co1.4Al0.8 rather than Mn2CoAl. Although conventional X-ray diffraction suggested the formation of single phase with XA/L21 strcture, a disk-shaped Mn-rich precipitate phase was observed in both annealed stoichiometric and Co-rich Mn2CoAl alloys along with the Mn1.8Co1.4Al0.8 main phase. Atomically resolved energy-dispersive X-ray spectroscopy mappings revealed that the Mn1.8Co1.4Al0.8 phase has a disordered inverse XA Heusler structure with Mn (A) and Al (C) sites partially substituted by Co and Mn, respectively. First-principles calculations based on the observed disordered structure suggest that the Heusler phase is not SGS but half-metallic. However, both annealed stoichiometric and Co-rich Mn2CoAl exhibit semiconducting-like resistivity and low anomalous Hall conductivity. These transport properties were regarded as the signatures of SGS in the previous studies; however, it could be due to localization of charged carriers due to the intersection of the Fermi level with Mn 3d and Co 3d states in Mn1.8Co1.4Al0.8. This study demonstrates that not only measurements of transport properties but also careful microstructure inspections are essential to validate SGS properties in the theoretically predicted SGS candidates among Heusler compounds.

AB - We report a detailed analysis of microstructure, magnetic and transport properties of a stoichiometric Mn2CoAl Heusler alloy, which has been predicted to be a spin-gapless semiconductor (SGS). Microstructure analysis revealed that the main phase was Mn1.8Co1.4Al0.8 rather than Mn2CoAl. Although conventional X-ray diffraction suggested the formation of single phase with XA/L21 strcture, a disk-shaped Mn-rich precipitate phase was observed in both annealed stoichiometric and Co-rich Mn2CoAl alloys along with the Mn1.8Co1.4Al0.8 main phase. Atomically resolved energy-dispersive X-ray spectroscopy mappings revealed that the Mn1.8Co1.4Al0.8 phase has a disordered inverse XA Heusler structure with Mn (A) and Al (C) sites partially substituted by Co and Mn, respectively. First-principles calculations based on the observed disordered structure suggest that the Heusler phase is not SGS but half-metallic. However, both annealed stoichiometric and Co-rich Mn2CoAl exhibit semiconducting-like resistivity and low anomalous Hall conductivity. These transport properties were regarded as the signatures of SGS in the previous studies; however, it could be due to localization of charged carriers due to the intersection of the Fermi level with Mn 3d and Co 3d states in Mn1.8Co1.4Al0.8. This study demonstrates that not only measurements of transport properties but also careful microstructure inspections are essential to validate SGS properties in the theoretically predicted SGS candidates among Heusler compounds.

KW - Heusler alloys

KW - Microstructure

KW - Phase stability

KW - Spin-gapless semiconductor

KW - Transport properties

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DO - 10.1016/j.actamat.2019.06.047

M3 - Article

AN - SCOPUS:85068425744

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JO - Acta Materialia

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