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127 results on '"Umetsu, R. Y."'

1. New type of half-metallic fully compensated ferrimagnet

Author

Semboshi, S., Umetsu, R. Y., Kawahito, Y., and Akai, H.

Subjects
Condensed Matter - Materials Science
Abstract

Half-metallic fully compensated ferrimagnets (HM-FCFMs), a special class of half-metals exhibiting zero magnetization at absolute zero, are promising candidates for next-generation spintronics applications. For over 25 years, theoretical studies have been conducted to realize HM-FCFM materials for practical applications. Herein, we experimentally demonstrate a NiAs-type hexagonal-structured (CrFe)S compound that could serve as an HM-FCFM material. It has a half-metallic nature, with 100% spin-polarized Fermi surfaces and zero magnetization. Further, the magnetization shows a linear behavior as a function of the magnetic field below the compensation temperature of around 200 K, with high magnetic coercivity of 38 kOe at 300 K. These magnetic features are expected to contribute to a quantum leap in the application of HM-FCFM layers in spintronics devices., Comment: 9 figures, 1 table

Published
2021

2. Half-metallicity of Mn2VAl ferrimagnet revealed by resonant inelastic soft x-ray scattering under magnetic field

Author

Umetsu, R. Y., Fujiwara, H., Nagai, K., Nakatani, Y., Kawada, M., Sekiyama, A., Kuroda, F., Fujii, H., Oguchi, T., Harada, Y., Miyawaki, J., and Suga, S.

Subjects
Condensed Matter - Materials Science
Abstract

Detailed information on the electronic states of both V and Mn 3d electrons in the ferrimagnet Mn2VAl is obtained by the bulk sensitive resonant inelastic soft x-ray scattering (SX-RIXS) excited with the circularly polarized light under an external magnetic field for the first time. The results under the V L-edge excitation have revealed the negligible partial density of states (PDOS) of the V 3d states around the Fermi energy as well as their rather localized character. Under the Mn L-edge excitation, on the other hand, the spectra are dominated by fluorescence with clear magnetic circular dichroism with noticeable excitation photon energy dependence. Compared with the theoretical prediction of the RIXS spectra based on the density-functional-theory band structure calculation, an itinerant, spin-dependent character of the Mn 3d states and decays of the Mn 2p core states are confirmed in consistence with the half-metallicity of the Mn 3d states.

Published
2018
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4. Electronic Structure and Magnetic Properties of Half-metallic Ferrimagnet Mn$_{2}$VAl Probed by Soft X-ray Spectroscopies

Author

Nagai, K., Fujiwara, H., Aratani, H., Fujioka, S., Yomosa, H., Nakatani, Y., Kiss, T., Sekiyama, A., Kuroda, F., Fujii, H., Oguchi, T., Tanaka, A., Miyawaki, J., Harada, Y., Takeda, Y., Saitoh, Y., Suga, S., and Umetsu, R. Y.

Subjects
Condensed Matter - Strongly Correlated Electrons
Abstract

We have studied the electronic structure of ferrimagnetic Mn2VAl single crystal by means of soft X-ray absorption spectroscopy (XAS), X-ray absorption magnetic circular dichroism (XMCD) and resonant soft X-ray inelastic scattering (RIXS). We have successfully observed the XMCD signals for all constitute elements, supporting the spin polarized states at the Fermi level. The Mn $L_{2,3}$ XAS and XMCD spectra are reproduced by the spectral simulation based on density-functional theory (DFT), indicating itinerant character of the Mn 3d states. On the other hand, V $3d$ electrons are rather localized since the ionic model can qualitatively explain the V $L_{2,3}$ XAS and XMCD spectra as well as the local dd excitation revealed by V $L_3$ RIXS., Comment: 9 pages, 9 figures

Published
2017
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6. Effect of disorder and vacancy defects on electrical transport properties of Co2MnGa thin films grown by magnetron sputtering.

Author

Miyashita, A., Maekawa, M., Suzuki, C., Yamamoto, S., Kawasuso, A., Wang, J., Seki, T., Umetsu, R. Y., and Takanashi, K.

Subjects
THIN films, ANOMALOUS Hall effect, POSITRON annihilation, CARBON dioxide, MAGNETRON sputtering, X-ray diffraction
Abstract

Co 2 MnGa is known as a Weyl semimetal exhibiting giant anomalous Hall and Nernst effects. However, the performance of Co 2 MnGa thin films grown on MgO(001) by the magnetron sputtering method is somewhat lower than that of the bulk crystals. Here, we attempted to improve the electrical transport properties by post-growth annealing at temperatures from 573 to 773 K. X-ray diffraction analysis indicated that the degree of long-range order changed from A 2 to B 2 plus L 2 1 upon annealing at 673 K or above. Positron annihilation spectroscopy revealed the presence of high-density (≳ 100 ppm) divacancies, which were absent in the bulk crystal, and their partial improvement near the Co 2 MnGa/MgO interface on annealing at 673 K or above. Accompanying these structural changes, the longitudinal and anomalous Hall conductivities increased considerably and the anomalous Hall angle reached a maximum value of 11.8%. These findings imply that the post-growth annealing improved the electrical transport properties of Co 2 MnGa films through the development of long-range crystal order and reduction of divacancies. However, the electrical performance achieved by thermal annealing was still insufficient in comparison with the bulk crystals, and hence for further improvement, alternative approaches may need to be considered. [ABSTRACT FROM AUTHOR]

Published
2021
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9. Electronic structure and magnetic properties of the half-metallic ferrimagnetMn2VAlprobed by soft x-ray spectroscopies

Author

Nagai, K., primary, Fujiwara, H., additional, Aratani, H., additional, Fujioka, S., additional, Yomosa, H., additional, Nakatani, Y., additional, Kiss, T., additional, Sekiyama, A., additional, Kuroda, F., additional, Fujii, H., additional, Oguchi, T., additional, Tanaka, A., additional, Miyawaki, J., additional, Harada, Y., additional, Takeda, Y., additional, Saitoh, Y., additional, Suga, S., additional, and Umetsu, R. Y., additional

Published
2018
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10. 軟X線分光で調べたハーフメタルフェリ磁性体Mn2VAlの電子構造と磁性

Author

Nagai, Keiji, Fujiwara, H., Aratani, H., Fujioka, Shinsuke, Yomosa, H., Nakatani, Y., Kiss, T., Sekiyama, A., Kuroda, F., Fujii, H., Oguchi, T., Tanaka, A., Miyawaki, J., Harada, Y., Takeda, Y., Saitoh, Y., Suga, S., and Umetsu, R. Y.

Abstract

金沢大学先端科学・社会共創推進機構, We have studied the electronic structure of ferrimagnetic Mn2VAl single crystals by means of soft x-ray absorption spectroscopy (XAS), x-ray absorption magnetic circular dichroism (XMCD), and resonant soft x-ray inelastic scattering (RIXS). We have successfully observed the XMCD signals for all the constituent elements. The Mn L2,3 XAS and XMCD spectra are reproduced by spectral simulations based on density-functional theory, indicating the itinerant character of the Mn 3d states. On the other hand, the V 3d electrons are rather localized since the ionic model can qualitatively explain the V L2,3 XAS and XMCD spectra. This picture is consistent with local dd excitations revealed by the V L3 RIXS. © 2018 American Physical Society.

Published
2018

15. Magnetic properties and stability of L21 and B2 phases in the Co2MnAl Heusler alloy.

Author

Umetsu, R. Y., Kobayashi, K., Fujita, A., Kainuma, R., and Ishida, K.

Abstract

Magnetic properties and stability of L21 and B2 phases in the Co2MnAl Heusler alloy were investigated. It was confirmed that the order-disorder transition from the B2 to L21 phase is located at about 950 K and that the Curie temperature TC of the L21 phase is 726 K which is about 50 K higher than that (TC=677 K) of the B2 phase. The difference in TC between the L21 and B2 phases is smaller than a theoretical prediction. On the other hand, the saturation magnetic moments Ms at 4.2 K for the L21 and B2 phases were estimated to be 4.07μB/f.u. and 4.16μB/f.u., respectively, comparable to the value Mt=4 expected from the generalized Slater–Pauling relation. [ABSTRACT FROM AUTHOR]

Published
2008
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16. Concentration dependence of magnetic and electrical properties of gap-type antiferromagnetic MnPt alloys.

Author

Umetsu, R. Y., Fukamichi, K., and Sakuma, A.

Subjects
*MANGANESE compounds, *PHYSICS
Abstract

Concentration dependence of the magnetic and electrical properties of MnPt alloy system with a AuCu-I type crystal structure has been investigated in order to discuss the electronic state. Temperature dependence of the electrical resistivity shows a characteristic behavior of gap-type antiferromagnets and the electronic specific heat coefficient y is considerably small in consistent with the calculated band structure having a pseudo-gap around the Fermi level. In the vicinity of the equiatomic composition, the Néel temperature is highest, whereas the value of y is smallest and increases with decreasing the Néel temperature. From the present experimental results, a close relationship between the electronic state and the antiferromagnetic stability in this alloy system is revealed, in accord with the band calculations. [ABSTRACT FROM AUTHOR]

Published
2002
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47. Pd–In–Fe shape memory alloy

Author

Ishikawa, H., primary, Sutou, Y., additional, Omori, T., additional, Oikawa, K., additional, Ishida, K., additional, Yoshikawa, A., additional, Umetsu, R. Y., additional, and Kainuma, R., additional

Published
2007
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