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Atomic Order of Multi-Element Alloy Distinguished by “Selecting” Wavelength of Synchrotron Radiation – Bringing out the Full Performance of Spin-Gapless Semiconductors (Press Release)

Release Date
14 Jun, 2022
  • BL13XU (X-ray Diffraction and Scattering I)

14 June 2022
Japan Synchrotron Radiation Research Institute (JASRI)
Osaka University

A research group led by Hiroo Tajiri (senior scientist) of Japan Synchrotron Radiation Research Institute (JASRI), Kohei Hamaya (professor) of Osaka University Graduate School of Engineering Science, Kenji Ueda (associate professor) of Nagoya University (currently professor at Waseda University), and Yuya Sakuraba (group leader) and Kazuhiro Hono (fellow) of the National Institute for Materials Science has fabricated Mn2CoAl alloy thin films (ternary Heusler alloy*1 thin films) using three typical film growth techniques. Ternary Heusler alloy thin films are promising candidates for spin-gapless semiconductors*2 expected to be used for spintronics applications*3. This research group has comprehensively evaluated the relationship between the performance and structure of these thin films using beamline BL13XU of the large synchrotron radiation facility SPring-8*4. The degree of order in an ordered alloy is directly linked to the performance of the material. This research group has also quantified the degree of order in ternary Heusler ordered alloy thin films with a complex structure through measurements including anomalous X-ray diffraction*5, which uses the wavelength selectivity of synchrotron radiation. The technique used in this study will enable the design and evaluation of various ordered alloy materials including Heusler alloys. The conventional research on spin-gapless semiconductors has focused on property determination. However, the achievements of this study clearly indicate that information about the crystal structure of thin films is extremely important to bring out the essential characteristics of spin-gapless semiconductors. These achievements provide new guidelines for the development of spin-gapless semiconductors that can be applied to energy-saving non-volatile memories.

The achievements of this study were published in Acta Materialia, an international scientific journal based in the United Kingdom, on 10 June 2022.

【Publication information】
Title: Structural insight using anomalous XRD into Mn2CoAl Heusler alloy films grown by magnetron sputtering, IBAS, and MBE techniques
Authors: Hiroo Tajiri, Loku Singgappulige Rosantha Kumara, Yuya Sakuraba, Zixi Chen, Jian Wang, Weinan Zhou, Kushuwaha Varun, Kenji Ueda, Shinya Yamada, Kohei Hayama, and Kazuhiro Hono
Journal: Acta Materialia
DOI: 10.1016/j.actamat.2022.118063

Figure1:Schematic diagrams of spin-gapless semiconductor and anomalous X-ray diffraction

Figure 1:Schematic diagrams of spin-gapless semiconductor and anomalous X-ray diffraction. It was expected that the alloy thin film with spin-gapless semiconducting characteristics grown by molecular beam epitaxy in this study would have the XA structure. However, the image from a scanning transmission electron microscope showed that the film consists of two crystalline phases of similar compositions. According to anomalous X-ray diffraction, which can distinguish between different elements, the film exhibits disordered structures in which Co and Mn are interchanged with each other instead of the XA structure.

Figure2:Results of anomalous X-ray diffraction analysis (top) and determined crystal structures (bottom)

Figure 2:Results of anomalous X-ray diffraction analysis (top) and determined crystal structures (bottom).


*1. Heusler alloys
Heusler alloys are typical ordered alloys with the molecular formula X2YZ. Half-Heusler alloys with the molecular formula XYZ have also been studied for a long time. Since 1903, when Friedrich Heusler reported that an alloy composed of three elements, non-magnetic Cu, Mn, and Al, exhibits ferromagnetic properties, various unique magnetic properties of Heusler alloys have been discovered. These include half-metallic properties, the magnetoresistance effect, magnetostriction, magnetic refrigeration, and shape memory effect. Heusler alloys have been studied and applied in a wide variety of areas including spintronics.

*2. Spin-gapless semiconductors
In the band theory of solids, materials with conduction electrons that are 100% spin-polarized are called half metals. Materials having semiconductive properties in addition to half-metallic properties are called spin-gapless semiconductors. Spin-gapless semiconductors are attracting attention as materials for spintronics devices because of their high polarizability and high mobility.

*3. Spintronics
Spintronics is an area of research targeting the technological application of both the electric charges and the spins representing the internal degrees of freedom of electrons in a solid material. Spintronics was coined from “spin” and “electronics”. Currently used spintronics devices include reading heads for hard discs featuring the giant magnetoresistance effect.

*4. Large synchrotron radiation facility SPring-8
SPring-8, owned by RIKEN, is a large synchrotron radiation facility that delivers some of the most powerful synchrotron radiations in the world. It is located in Harima Science Garden City, Hyogo Prefecture, Japan. JASRI supports users of the facility. The name “SPring-8” is derived from “Super Photon ring-8 GeV”. The research conducted at SPring-8 covers a wide range of fields including nanotechnology, biotechnology, and industrial applications.

*5. Anomalous X-ray diffraction
The scattering power of elements for X-rays of certain energies varies significantly owing to the resonance effect, which is known as the anomalous dispersion effect. Anomalous X-ray diffraction is a technique of measuring the X-ray energy dependence of the diffraction intensity of target elements using the wavelength selectivity (energy selectivity) of synchrotron radiation. Japanese scientists have contributed to this area since its early stages when the phenomenon of X-ray diffraction was discovered. In a well-known study, Dr. Shoji Nishikawa used anomalous X-ray diffraction to determine the polarity of non-centrosymmetric zinc sulfide crystals.


Hiroo Tajiri
Japan Synchrotron Radiation Research Institute (JASRI)
Scattering and Imaging Division (senior scientist)
 TEL:+81-791-58-0802 (ext:3443)

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